BASH(1)                                                                                                                                BASH(1)

NAME

       bash - GNU Bourne-Again SHell

SYNOPSIS

       bash [options] [file]

COPYRIGHT

       Bash is Copyright (C) 1989-2011 by the Free Software Foundation, Inc.

DESCRIPTION

       Bash  is  an  sh-compatible command language interpreter that executes commands read from the standard input or from a file.  Bash also
       incorporates useful features from the Korn and C shells (ksh and csh).

       Bash is intended to be a conformant implementation of the Shell and Utilities portion of the IEEE POSIX  specification  (IEEE  Standard
       1003.1).  Bash can be configured to be POSIX-conformant by default.

OPTIONS

       All  of  the   single-character  shell options documented in the description of the set builtin command can be used as options when the
       shell is invoked.  In addition, bash interprets the following options when it is invoked:

       -c string If the -c option is present, then commands are read from string.  If there are arguments after the string, they are  assigned
                 to the positional parameters, starting with $0.
       -i        If the -i option is present, the shell is interactive.
       -l        Make bash act as if it had been invoked as a login shell (see INVOCATION below).
       -r        If the -r option is present, the shell becomes restricted (see RESTRICTED SHELL below).
       -s        If  the  -s  option  is  present, or if no arguments remain after option processing, then commands are read from the standard
                 input.  This option allows the positional parameters to be set when invoking an interactive shell.
       -D        A list of all double-quoted strings preceded by $ is printed on the standard output.  These are the strings that are  subject
                 to language translation when the current locale is not C or POSIX.  This implies the -n option; no commands will be executed.
       [-+]O [shopt_option]
                 shopt_option  is  one of the shell options accepted by the shopt builtin (see SHELL BUILTIN COMMANDS below).  If shopt_option
                 is present, -O sets the value of that option; +O unsets it.  If shopt_option is not supplied, the names  and  values  of  the
                 shell  options accepted by shopt are printed on the standard output.  If the invocation option is +O, the output is displayed
                 in a format that may be reused as input.
       --        A -- signals the end of options and disables further option processing.  Any arguments after the -- are treated as  filenames
                 and arguments.  An argument of - is equivalent to --.

       Bash  also  interprets  a number of multi-character options.  These options must appear on the command line before the single-character
       options to be recognized.

       --debugger
              Arrange for the debugger profile to be executed before the shell starts.  Turns on extended debugging mode (see the  description
              of the extdebug option to the shopt builtin below).
       --dump-po-strings
              Equivalent to -D, but the output is in the GNU gettext po (portable object) file format.
       --dump-strings
              Equivalent to -D.
       --help Display a usage message on standard output and exit successfully.
       --init-file file
       --rcfile file
              Execute  commands  from  file  instead  of  the  system  wide  initialization  file  /etc/bash.bashrc  and the standard personal
              initialization file ~/.bashrc if the shell is interactive (see INVOCATION below).

       --login
              Equivalent to -l.

       --noediting
              Do not use the GNU readline library to read command lines when the shell is interactive.

       --noprofile
              Do not read either the system-wide startup file /etc/profile or  any  of  the  personal  initialization  files  ~/.bash_profile,
              ~/.bash_login, or ~/.profile.  By default, bash reads these files when it is invoked as a login shell (see INVOCATION below).

       --norc Do  not  read and execute the system wide initialization file /etc/bash.bashrc and the personal initialization file ~/.bashrc if
              the shell is interactive.  This option is on by default if the shell is invoked as sh.

       --posix
              Change the behavior of bash where the default operation differs from the POSIX standard to match the standard (posix mode).

       --restricted
              The shell becomes restricted (see RESTRICTED SHELL below).

       --verbose
              Equivalent to  -v.

       --version
              Show version information for this instance of bash on the standard output and exit successfully.

ARGUMENTS

       If arguments remain after option processing, and neither the -c nor the -s option has been supplied, the first argument is  assumed  to
       be  the  name  of  a  file  containing  shell commands.  If bash is invoked in this fashion, $0 is set to the name of the file, and the
       positional parameters are set to the remaining arguments.  Bash reads and executes commands from this file, then  exits.   Bash's  exit
       status  is  the exit status of the last command executed in the script.  If no commands are executed, the exit status is 0.  An attempt
       is first made to open the file in the current directory, and, if no file is found, then the shell searches the directories in PATH  for
       the script.

INVOCATION

       A login shell is one whose first character of argument zero is a -, or one started with the --login option.

       An  interactive  shell  is  one  started without non-option arguments and without the -c option whose standard input and error are both
       connected to terminals (as determined by isatty(3)), or one started with the -i option.  PS1 is set  and  $-  includes  i  if  bash  is
       interactive, allowing a shell script or a startup file to test this state.

       The  following  paragraphs describe how bash executes its startup files.  If any of the files exist but cannot be read, bash reports an
       error.  Tildes are expanded in file names as described below under Tilde Expansion in the EXPANSION section.

       When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and  executes
       commands  from  the  file /etc/profile, if that file exists.  After reading that file, it looks for ~/.bash_profile, ~/.bash_login, and
       ~/.profile, in that order, and reads and executes commands from the first one that exists and is readable.  The --noprofile option  may
       be used when the shell is started to inhibit this behavior.

       When a login shell exits, bash reads and executes commands from the file ~/.bash_logout, if it exists.

       When  an  interactive shell that is not a login shell is started, bash reads and executes commands from /etc/bash.bashrc and ~/.bashrc,
       if these files exist.  This may be inhibited by using the --norc option.  The --rcfile file option will force bash to read and  execute
       commands from file instead of /etc/bash.bashrc and ~/.bashrc.

       When  bash  is  started  non-interactively,  to run a shell script, for example, it looks for the variable BASH_ENV in the environment,
       expands its value if it appears there, and uses the expanded value as the name of a file to read and execute.  Bash behaves as  if  the
       following command were executed:
              if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
       but the value of the PATH variable is not used to search for the file name.

       If  bash is invoked with the name sh, it tries to mimic the startup behavior of historical versions of sh as closely as possible, while
       conforming to the POSIX standard as well.  When invoked as an interactive login shell, or a  non-interactive  shell  with  the  --login
       option,  it first attempts to read and execute commands from /etc/profile and ~/.profile, in that order.  The --noprofile option may be
       used to inhibit this behavior.  When invoked as an interactive shell with the name sh, bash looks for the  variable  ENV,  expands  its
       value  if  it  is defined, and uses the expanded value as the name of a file to read and execute.  Since a shell invoked as sh does not
       attempt to read and execute commands from any other startup files, the --rcfile option has no effect.  A non-interactive shell  invoked
       with  the name sh does not attempt to read any other startup files.  When invoked as sh, bash enters posix mode after the startup files
       are read.

       When bash is started in posix mode, as with the --posix command line option, it follows the POSIX standard for startup files.  In  this
       mode, interactive shells expand the ENV variable and commands are read and executed from the file whose name is the expanded value.  No
       other startup files are read.

       Bash attempts to determine when it is being run with its standard input connected to a network connection,  as  when  executed  by  the
       remote  shell  daemon, usually rshd, or the secure shell daemon sshd.  If bash determines it is being run in this fashion, it reads and
       executes commands from ~/.bashrc and ~/.bashrc, if these files exist and are readable.  It will not do this  if  invoked  as  sh.   The
       --norc option may be used to inhibit this behavior, and the --rcfile option may be used to force another file to be read, but rshd does
       not generally invoke the shell with those options or allow them to be specified.

       If the shell is started with the effective user (group) id not equal to the real user (group) id, and the -p option is not supplied, no
       startup  files  are  read,  shell  functions  are  not  inherited from the environment, the SHELLOPTS, BASHOPTS, CDPATH, and GLOBIGNORE
       variables, if they appear in the environment, are ignored, and the effective user id is set to the real user id.  If the -p  option  is
       supplied at invocation, the startup behavior is the same, but the effective user id is not reset.

DEFINITIONS

       The following definitions are used throughout the rest of this document.
       blank  A space or tab.
       word   A sequence of characters considered as a single unit by the shell.  Also known as a token.
       name   A  word consisting only of alphanumeric characters and underscores, and beginning with an alphabetic character or an underscore.
              Also referred to as an identifier.
       metacharacter
              A character that, when unquoted, separates words.  One of the following:
              |  & ; ( ) < > space tab
       control operator
              A token that performs a control function.  It is one of the following symbols:
              || & && ; ;; ( ) | |& <newline>

RESERVED WORDS

       Reserved words are words that have a special meaning to the shell.  The following words are recognized as reserved  when  unquoted  and
       either the first word of a simple command (see SHELL GRAMMAR below) or the third word of a case or for command:

       ! case  do done elif else esac fi for function if in select then until while { } time [[ ]]

SHELL GRAMMAR

   Simple Commands
       A simple command is a sequence of optional variable assignments followed by blank-separated words and redirections, and terminated by a
       control operator.  The first word specifies the command to be executed, and is passed as argument zero.  The remaining words are passed
       as arguments to the invoked command.

       The return value of a simple command is its exit status, or 128+n if the command is terminated by signal n.

   Pipelines
       A pipeline is a sequence of one or more commands separated by one of the control operators | or |&.  The format for a pipeline is:

              [time [-p]] [ ! ] command [ [||&] command2 ... ]

       The  standard  output  of  command  is connected via a pipe to the standard input of command2.  This connection is performed before any
       redirections specified by the command (see REDIRECTION below).  If |& is used, the standard error of command is connected to command2's
       standard  input  through  the pipe; it is shorthand for 2>&1 |.  This implicit redirection of the standard error is performed after any
       redirections specified by the command.

       The return status of a pipeline is the exit status of the last command, unless the pipefail option is enabled.  If pipefail is enabled,
       the  pipeline's return status is the value of the last (rightmost) command to exit with a non-zero status, or zero if all commands exit
       successfully.  If the reserved word !  precedes a pipeline, the exit status of that pipeline is the logical negation of the exit status
       as described above.  The shell waits for all commands in the pipeline to terminate before returning a value.

       If  the time reserved word precedes a pipeline, the elapsed as well as user and system time consumed by its execution are reported when
       the pipeline terminates.  The -p option changes the output format to that specified by POSIX.  When the shell is in posix mode, it does
       not  recognize time as a reserved word if the next token begins with a `-'.  The TIMEFORMAT variable may be set to a format string that
       specifies how the timing information should be displayed; see the description of TIMEFORMAT under Shell Variables below.

       When the shell is in posix mode, time may be followed by a newline.  In this case, the shell displays the total user  and  system  time
       consumed by the shell and its children.  The TIMEFORMAT variable may be used to specify the format of the time information.

       Each command in a pipeline is executed as a separate process (i.e., in a subshell).

   Lists
       A list is a sequence of one or more pipelines separated by one of the operators ;, &, &&, or ||, and optionally terminated by one of ;,
       &, or <newline>.

       Of these list operators, && and || have equal precedence, followed by ; and &, which have equal precedence.

       A sequence of one or more newlines may appear in a list instead of a semicolon to delimit commands.

       If a command is terminated by the control operator &, the shell executes the command in the background in a subshell.  The  shell  does
       not  wait  for the command to finish, and the return status is 0.  Commands separated by a ; are executed sequentially; the shell waits
       for each command to terminate in turn.  The return status is the exit status of the last command executed.

       AND and OR lists are sequences of one of more pipelines separated by the && and || control operators, respectively.  AND and  OR  lists
       are executed with left associativity.  An AND list has the form

              command1 && command2

       command2 is executed if, and only if, command1 returns an exit status of zero.

       An OR list has the form

              command1 || command2

       command2  is executed if and only if command1 returns a non-zero exit status.  The return status of AND and OR lists is the exit status
       of the last command executed in the list.

   Compound Commands
       A compound command is one of the following:

       (list) list is executed in a subshell environment (see COMMAND EXECUTION ENVIRONMENT below).  Variable assignments and builtin commands
              that  affect  the shell's environment do not remain in effect after the command completes.  The return status is the exit status
              of list.

       { list; }
              list is simply executed in the current shell environment.  list must be terminated with a newline or semicolon.  This  is  known
              as  a  group  command.   The return status is the exit status of list.  Note that unlike the metacharacters ( and ), { and } are
              reserved words and must occur where a reserved word is permitted to be recognized.  Since they do not cause a word  break,  they
              must be separated from list by whitespace or another shell metacharacter.

       ((expression))
              The  expression is evaluated according to the rules described below under ARITHMETIC EVALUATION.  If the value of the expression
              is non-zero, the return status is 0; otherwise the return status is 1.  This is exactly equivalent to let "expression".

       [[ expression ]]
              Return a status of 0 or 1 depending on the evaluation of the conditional expression expression.  Expressions are composed of the
              primaries  described  below under CONDITIONAL EXPRESSIONS.  Word splitting and pathname expansion are not performed on the words
              between the [[ and ]]; tilde expansion, parameter and variable expansion, arithmetic expansion,  command  substitution,  process
              substitution, and quote removal are performed.  Conditional operators such as -f must be unquoted to be recognized as primaries.

              When used with [[, the < and > operators sort lexicographically using the current locale.

       See  the  description  of the test builtin command (section SHELL BUILTIN COMMANDS below) for the handling of parameters (i.e.  missing
       parameters).

       When the == and != operators are used, the string to the right of the operator is considered a pattern and  matched  according  to  the
       rules described below under Pattern Matching.  If the shell option nocasematch is enabled, the match is performed without regard to the
       case of alphabetic characters.  The return value is 0 if the string matches (==) or does not match (!=) the pattern, and  1  otherwise.
       Any part of the pattern may be quoted to force it to be matched as a string.

       An  additional  binary  operator, =~, is available, with the same precedence as == and !=.  When it is used, the string to the right of
       the operator is considered an extended regular expression and matched accordingly (as in regex(3)).  The  return  value  is  0  if  the
       string matches the pattern, and 1 otherwise.  If the regular expression is syntactically incorrect, the conditional expression's return
       value is 2.  If the shell option nocasematch is enabled, the match is performed without regard to the case  of  alphabetic  characters.
       Any part of the pattern may be quoted to force it to be matched as a string.  Substrings matched by parenthesized subexpressions within
       the regular expression are saved in the array variable BASH_REMATCH.  The element of BASH_REMATCH with index 0 is the  portion  of  the
       string  matching the entire regular expression.  The element of BASH_REMATCH with index n is the portion of the string matching the nth
       parenthesized subexpression.

       Expressions may be combined using the following operators, listed in decreasing order of precedence:

              ( expression )
                     Returns the value of expression.  This may be used to override the normal precedence of operators.
              ! expression
                     True if expression is false.
              expression1 && expression2
                     True if both expression1 and expression2 are true.
              expression1 || expression2
                     True if either expression1 or expression2 is true.

              The && and || operators do not evaluate expression2 if the value of expression1 is sufficient to determine the return  value  of
              the entire conditional expression.

       for name [ [ in [ word ... ] ] ; ] do list ; done
              The  list  of words following in is expanded, generating a list of items.  The variable name is set to each element of this list
              in turn, and list is executed each time.  If the in word is omitted, the for command executes  list  once  for  each  positional
              parameter  that  is set (see PARAMETERS below).  The return status is the exit status of the last command that executes.  If the
              expansion of the items following in results in an empty list, no commands are executed, and the return status is 0.

       for (( expr1 ; expr2 ; expr3 )) ; do list ; done
              First, the arithmetic expression expr1 is evaluated according to the rules described below  under  ARITHMETIC  EVALUATION.   The
              arithmetic  expression  expr2  is then evaluated repeatedly until it evaluates to zero.  Each time expr2 evaluates to a non-zero
              value, list is executed and the arithmetic expression expr3 is evaluated.  If any expression is omitted, it  behaves  as  if  it
              evaluates  to  1.   The  return  value  is  the exit status of the last command in list that is executed, or false if any of the
              expressions is invalid.

       select name [ in word ] ; do list ; done
              The list of words following in is expanded, generating a list of items.  The set of expanded words is printed  on  the  standard
              error, each preceded by a number.  If the in word is omitted, the positional parameters are printed (see PARAMETERS below).  The
              PS3 prompt is then displayed and a line read from the standard input.  If the line consists of a number corresponding to one  of
              the  displayed  words,  then  the  value  of name is set to that word.  If the line is empty, the words and prompt are displayed
              again.  If EOF is read, the command completes.  Any other value read causes name to be set to null.  The line read is  saved  in
              the  variable REPLY.  The list is executed after each selection until a break command is executed.  The exit status of select is
              the exit status of the last command executed in list, or zero if no commands were executed.

       case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
              A case command first expands word, and tries to match it against each pattern in turn, using the  same  matching  rules  as  for
              pathname  expansion  (see  Pathname  Expansion  below).   The  word  is  expanded  using tilde expansion, parameter and variable
              expansion, arithmetic substitution, command substitution, process substitution and quote  removal.   Each  pattern  examined  is
              expanded  using  tilde  expansion,  parameter and variable expansion, arithmetic substitution, command substitution, and process
              substitution.  If the shell option nocasematch is enabled, the match is performed without  regard  to  the  case  of  alphabetic
              characters.   When  a match is found, the corresponding list is executed.  If the ;; operator is used, no subsequent matches are
              attempted after the first pattern match.  Using ;& in place of ;; causes execution to continue with the list associated with the
              next  set  of  patterns.   Using ;;& in place of ;; causes the shell to test the next pattern list in the statement, if any, and
              execute any associated list on a successful match.  The exit status is zero if no pattern matches.  Otherwise, it  is  the  exit
              status of the last command executed in list.

       if list; then list; [ elif list; then list; ] ... [ else list; ] fi
              The if list is executed.  If its exit status is zero, the then list is executed.  Otherwise, each elif list is executed in turn,
              and if its exit status is zero, the corresponding then list is executed and the command completes.  Otherwise, the else list  is
              executed, if present.  The exit status is the exit status of the last command executed, or zero if no condition tested true.

       while list-1; do list-2; done
       until list-1; do list-2; done
              The while command continuously executes the list list-2 as long as the last command in the list list-1 returns an exit status of
              zero.  The until command is identical to the while command, except that the test is negated; list-2 is executed as long  as  the
              last  command  in  list-1 returns a non-zero exit status.  The exit status of the while and until commands is the exit status of
              the last command executed in list-2, or zero if none was executed.

   Coprocesses
       A coprocess is a shell command preceded by the coproc reserved word.  A coprocess is executed asynchronously in a subshell, as  if  the
       command had been terminated with the & control operator, with a two-way pipe established between the executing shell and the coprocess.

       The format for a coprocess is:

              coproc [NAME] command [redirections]

       This  creates  a coprocess named NAME.  If NAME is not supplied, the default name is COPROC.  NAME must not be supplied if command is a
       simple command (see above); otherwise, it is interpreted as the first word of the simple command.  When the  coproc  is  executed,  the
       shell creates an array variable (see Arrays below) named NAME in the context of the executing shell.  The standard output of command is
       connected via a pipe to a file descriptor in the executing shell, and that file descriptor is assigned to NAME[0].  The standard  input
       of  command is connected via a pipe to a file descriptor in the executing shell, and that file descriptor is assigned to NAME[1].  This
       pipe is established before any redirections specified by the command (see REDIRECTION below).  The file descriptors can be utilized  as
       arguments  to  shell  commands  and  redirections  using  standard word expansions.  The process ID of the shell spawned to execute the
       coprocess is available as the value of the variable NAME_PID.  The wait builtin command may be  used  to  wait  for  the  coprocess  to
       terminate.

       The return status of a coprocess is the exit status of command.

   Shell Function Definitions
       A  shell  function  is  an  object  that  is  called like a simple command and executes a compound command with a new set of positional
       parameters.  Shell functions are declared as follows:

       name () compound-command [redirection]
       function name [()] compound-command [redirection]
              This defines a function named name.  The reserved word function is optional.  If the function reserved  word  is  supplied,  the
              parentheses  are  optional.   The  body  of the function is the compound command compound-command (see Compound Commands above).
              That command is usually a list of commands between { and }, but may  be  any  command  listed  under  Compound  Commands  above.
              compound-command  is  executed  whenever  name  is specified as the name of a simple command.  Any redirections (see REDIRECTION
              below) specified when a function is defined are performed when the  function  is  executed.   The  exit  status  of  a  function
              definition  is  zero  unless a syntax error occurs or a readonly function with the same name already exists.  When executed, the
              exit status of a function is the exit status of the last command executed in the body.  (See FUNCTIONS below.)

COMMENTS

       In a non-interactive shell, or an interactive shell in which the interactive_comments option to the shopt builtin is enabled (see SHELL
       BUILTIN  COMMANDS  below),  a  word  beginning  with  #  causes  that word and all remaining characters on that line to be ignored.  An
       interactive shell without the interactive_comments option enabled does not allow comments.  The interactive_comments option  is  on  by
       default in interactive shells.

QUOTING

       Quoting  is  used  to  remove  the special meaning of certain characters or words to the shell.  Quoting can be used to disable special
       treatment for special characters, to prevent reserved words from being recognized as such, and to prevent parameter expansion.

       Each of the metacharacters listed above under DEFINITIONS has special meaning to the shell and must be quoted if  it  is  to  represent
       itself.

       When the command history expansion facilities are being used (see HISTORY EXPANSION below), the history expansion character, usually !,
       must be quoted to prevent history expansion.

       There are three quoting mechanisms: the escape character, single quotes, and double quotes.

       A non-quoted backslash (\) is the escape character.  It preserves the literal value of  the  next  character  that  follows,  with  the
       exception  of  <newline>.   If  a  \<newline> pair appears, and the backslash is not itself quoted, the \<newline> is treated as a line
       continuation (that is, it is removed from the input stream and effectively ignored).

       Enclosing characters in single quotes preserves the literal value of each character within the quotes.  A single quote  may  not  occur
       between single quotes, even when preceded by a backslash.

       Enclosing  characters  in double quotes preserves the literal value of all characters within the quotes, with the exception of $, `, \,
       and, when history expansion is enabled, !.  The characters $ and ` retain their special meaning within double  quotes.   The  backslash
       retains  its  special  meaning  only when followed by one of the following characters: $, `, ", \, or <newline>.  A double quote may be
       quoted within double quotes by preceding it with a backslash.  If enabled, history expansion will be performed unless an  !   appearing
       in double quotes is escaped using a backslash.  The backslash preceding the !  is not removed.

       The special parameters * and @ have special meaning when in double quotes (see PARAMETERS below).

       Words of the form $'string' are treated specially.  The word expands to string, with backslash-escaped characters replaced as specified
       by the ANSI C standard.  Backslash escape sequences, if present, are decoded as follows:
              \a     alert (bell)
              \b     backspace
              \e
              \E     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \'     single quote
              \"     double quote
              \nnn   the eight-bit character whose value is the octal value nnn (one to three digits)
              \xHH   the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)
              \uHHHH the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHH (one to four hex digits)
              \UHHHHHHHH
                     the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHHHHHH (one to eight hex digits)
              \cx    a control-x character

       The expanded result is single-quoted, as if the dollar sign had not been present.

       A double-quoted string preceded by a dollar sign ($"string") will cause the string to be translated according to  the  current  locale.
       If  the current locale is C or POSIX, the dollar sign is ignored.  If the string is translated and replaced, the replacement is double-
       quoted.

PARAMETERS

       A parameter is an entity that stores values.  It can be a name, a number, or one of the special characters listed below  under  Special
       Parameters.  A variable is a parameter denoted by a name.  A variable has a value and zero or more attributes.  Attributes are assigned
       using the declare builtin command (see declare below in SHELL BUILTIN COMMANDS).

       A parameter is set if it has been assigned a value.  The null string is a valid value.  Once a variable is set, it may be unset only by
       using the unset builtin command (see SHELL BUILTIN COMMANDS below).

       A variable may be assigned to by a statement of the form

              name=[value]

       If value is not given, the variable is assigned the null string.  All values undergo tilde expansion, parameter and variable expansion,
       command substitution, arithmetic expansion, and quote removal (see EXPANSION below).  If the variable has its  integer  attribute  set,
       then  value is evaluated as an arithmetic expression even if the $((...)) expansion is not used (see Arithmetic Expansion below).  Word
       splitting is not performed, with the exception of "$@" as  explained  below  under  Special  Parameters.   Pathname  expansion  is  not
       performed.   Assignment  statements  may  also  appear as arguments to the alias, declare, typeset, export, readonly, and local builtin
       commands.

       In the context where an assignment statement is assigning a value to a shell variable or array index, the += operator can  be  used  to
       append  to  or  add  to  the variable's previous value.  When += is applied to a variable for which the integer attribute has been set,
       value is evaluated as an arithmetic expression and added to the variable's current value, which is also evaluated.  When += is  applied
       to  an  array variable using compound assignment (see Arrays below), the variable's value is not unset (as it is when using =), and new
       values are appended to the array beginning at one greater than the array's maximum index (for indexed arrays) or  added  as  additional
       key-value  pairs  in  an associative array.  When applied to a string-valued variable, value is expanded and appended to the variable's
       value.

   Positional Parameters
       A positional parameter is a parameter denoted by one or more digits, other than the single digit 0.  Positional parameters are assigned
       from  the  shell's arguments when it is invoked, and may be reassigned using the set builtin command.  Positional parameters may not be
       assigned to with assignment statements.  The positional parameters are temporarily replaced when a  shell  function  is  executed  (see
       FUNCTIONS below).

       When a positional parameter consisting of more than a single digit is expanded, it must be enclosed in braces (see EXPANSION below).

   Special Parameters
       The shell treats several parameters specially.  These parameters may only be referenced; assignment to them is not allowed.
       *      Expands to the positional parameters, starting from one.  When the expansion occurs within double quotes, it expands to a single
              word with the value of each parameter separated by the first character of the IFS special variable.  That is, "$*" is equivalent
              to  "$1c$2c...", where c is the first character of the value of the IFS variable.  If IFS is unset, the parameters are separated
              by spaces.  If IFS is null, the parameters are joined without intervening separators.
       @      Expands to the positional parameters, starting from one.  When the expansion occurs within double quotes, each parameter expands
              to  a  separate  word.   That  is, "$@" is equivalent to "$1" "$2" ...  If the double-quoted expansion occurs within a word, the
              expansion of the first parameter is joined with the beginning part of the original word, and the expansion of the last parameter
              is  joined  with  the  last  part  of the original word.  When there are no positional parameters, "$@" and $@ expand to nothing
              (i.e., they are removed).
       #      Expands to the number of positional parameters in decimal.
       ?      Expands to the exit status of the most recently executed foreground pipeline.
       -      Expands to the current option flags as specified upon invocation, by the set builtin command, or those set by the  shell  itself
              (such as the -i option).
       $      Expands to the process ID of the shell.  In a () subshell, it expands to the process ID of the current shell, not the subshell.
       !      Expands to the process ID of the most recently executed background (asynchronous) command.
       0      Expands  to  the  name  of  the  shell or shell script.  This is set at shell initialization.  If bash is invoked with a file of
              commands, $0 is set to the name of that file.  If bash is started with the -c option, then $0 is set to the first argument after
              the  string  to be executed, if one is present.  Otherwise, it is set to the file name used to invoke bash, as given by argument
              zero.
       _      At shell startup, set to the absolute pathname used to invoke the shell  or  shell  script  being  executed  as  passed  in  the
              environment or argument list.  Subsequently, expands to the last argument to the previous command, after expansion.  Also set to
              the full pathname used to invoke each command executed and placed in the environment exported to that  command.   When  checking
              mail, this parameter holds the name of the mail file currently being checked.

   Shell Variables
       The following variables are set by the shell:

       BASH   Expands to the full file name used to invoke this instance of bash.
       BASHOPTS
              A  colon-separated  list  of  enabled  shell  options.  Each word in the list is a valid argument for the -s option to the shopt
              builtin command (see SHELL BUILTIN COMMANDS below).  The options appearing in BASHOPTS are those reported as on  by  shopt.   If
              this  variable  is  in  the  environment  when  bash starts up, each shell option in the list will be enabled before reading any
              startup files.  This variable is read-only.
       BASHPID
              Expands to the process ID of the current bash process.  This differs from $$ under certain circumstances, such as subshells that
              do not require bash to be re-initialized.
       BASH_ALIASES
              An  associative  array  variable  whose  members  correspond to the internal list of aliases as maintained by the alias builtin.
              Elements added to this array appear in the alias list; unsetting array elements cause aliases to be removed from the alias list.
       BASH_ARGC
              An array variable whose values are the number of parameters in each frame of the current bash execution call stack.  The  number
              of parameters to the current subroutine (shell function or script executed with . or source) is at the top of the stack.  When a
              subroutine is executed, the number of parameters passed is pushed onto  BASH_ARGC.   The  shell  sets  BASH_ARGC  only  when  in
              extended debugging mode (see the description of the extdebug option to the shopt builtin below)
       BASH_ARGV
              An  array  variable  containing all of the parameters in the current bash execution call stack.  The final parameter of the last
              subroutine call is at the top of the stack; the first parameter of the initial call is at the  bottom.   When  a  subroutine  is
              executed, the parameters supplied are pushed onto BASH_ARGV.  The shell sets BASH_ARGV only when in extended debugging mode (see
              the description of the extdebug option to the shopt builtin below)
       BASH_CMDS
              An associative array variable whose members correspond to the internal hash table of commands as maintained by the hash builtin.
              Elements  added  to  this  array  appear  in the hash table; unsetting array elements cause commands to be removed from the hash
              table.
       BASH_COMMAND
              The command currently being executed or about to be executed, unless the shell is executing a command as the result of  a  trap,
              in which case it is the command executing at the time of the trap.
       BASH_EXECUTION_STRING
              The command argument to the -c invocation option.
       BASH_LINENO
              An  array  variable  whose members are the line numbers in source files where each corresponding member of FUNCNAME was invoked.
              ${BASH_LINENO[$i]} is the  line  number  in  the  source  file  (${BASH_SOURCE[$i+1]})  where  ${FUNCNAME[$i]}  was  called  (or
              ${BASH_LINENO[$i-1]} if referenced within another shell function).  Use LINENO to obtain the current line number.
       BASH_REMATCH
              An  array variable whose members are assigned by the =~ binary operator to the [[ conditional command.  The element with index 0
              is the portion of the string matching the entire regular expression.  The element with index n is  the  portion  of  the  string
              matching the nth parenthesized subexpression.  This variable is read-only.
       BASH_SOURCE
              An  array  variable  whose  members  are the source filenames where the corresponding shell function names in the FUNCNAME array
              variable are defined.   The  shell  function  ${FUNCNAME[$i]}  is  defined  in  the  file  ${BASH_SOURCE[$i]}  and  called  from
              ${BASH_SOURCE[$i+1]}.
       BASH_SUBSHELL
              Incremented by one each time a subshell or subshell environment is spawned.  The initial value is 0.
       BASH_VERSINFO
              A  readonly  array  variable whose members hold version information for this instance of bash.  The values assigned to the array
              members are as follows:
              BASH_VERSINFO[0]        The major version number (the release).
              BASH_VERSINFO[1]        The minor version number (the version).
              BASH_VERSINFO[2]        The patch level.
              BASH_VERSINFO[3]        The build version.
              BASH_VERSINFO[4]        The release status (e.g., beta1).
              BASH_VERSINFO[5]        The value of MACHTYPE.
       BASH_VERSION
              Expands to a string describing the version of this instance of bash.
       COMP_CWORD
              An index into ${COMP_WORDS} of the word containing the current cursor position.   This  variable  is  available  only  in  shell
              functions invoked by the programmable completion facilities (see Programmable Completion below).
       COMP_KEY
              The key (or final key of a key sequence) used to invoke the current completion function.
       COMP_LINE
              The  current command line.  This variable is available only in shell functions and external commands invoked by the programmable
              completion facilities (see Programmable Completion below).
       COMP_POINT
              The index of the current cursor position relative to the beginning of the current command.  If the current cursor position is at
              the  end of the current command, the value of this variable is equal to ${#COMP_LINE}.  This variable is available only in shell
              functions and external commands invoked by the programmable completion facilities (see Programmable Completion below).
       COMP_TYPE
              Set to an integer value corresponding to the type of completion attempted that caused a completion function to be  called:  TAB,
              for normal completion, ?, for listing completions after successive tabs, !, for listing alternatives on partial word completion,
              @, to list completions if the word is not unmodified, or %, for menu completion.  This  variable  is  available  only  in  shell
              functions and external commands invoked by the programmable completion facilities (see Programmable Completion below).
       COMP_WORDBREAKS
              The  set  of characters that the readline library treats as word separators when performing word completion.  If COMP_WORDBREAKS
              is unset, it loses its special properties, even if it is subsequently reset.
       COMP_WORDS
              An array variable (see Arrays below) consisting of the individual words in the current command line.  The  line  is  split  into
              words  as readline would split it, using COMP_WORDBREAKS as described above.  This variable is available only in shell functions
              invoked by the programmable completion facilities (see Programmable Completion below).
       COPROC An array variable (see Arrays below) created to hold the file descriptors for output from and input to an unnamed coprocess (see
              Coprocesses above).
       DIRSTACK
              An array variable (see Arrays below) containing the current contents of the directory stack.  Directories appear in the stack in
              the order they are displayed by the dirs builtin.  Assigning to members of this array variable may be used to modify directories
              already  in  the stack, but the pushd and popd builtins must be used to add and remove directories.  Assignment to this variable
              will not change the current directory.  If DIRSTACK is unset, it loses its special properties, even if it is subsequently reset.
       EUID   Expands to the effective user ID of the current user, initialized at shell startup.  This variable is readonly.
       FUNCNAME
              An array variable containing the names of all shell functions currently in the execution call stack.  The element with  index  0
              is  the  name  of  any  currently-executing shell function.  The bottom-most element (the one with the highest index) is "main".
              This variable exists only when a shell function is executing.  Assignments to FUNCNAME  have  no  effect  and  return  an  error
              status.  If FUNCNAME is unset, it loses its special properties, even if it is subsequently reset.

              This  variable can be used with BASH_LINENO and BASH_SOURCE.  Each element of FUNCNAME has corresponding elements in BASH_LINENO
              and BASH_SOURCE to describe the call stack.  For instance, ${FUNCNAME[$i]} was called from the file ${BASH_SOURCE[$i+1]} at line
              number ${BASH_LINENO[$i]}.  The caller builtin displays the current call stack using this information.
       GROUPS An array variable containing the list of groups of which the current user is a member.  Assignments to GROUPS have no effect and
              return an error status.  If GROUPS is unset, it loses its special properties, even if it is subsequently reset.
       HISTCMD
              The history number, or index in the history list, of the current command.  If HISTCMD is unset, it loses its special properties,
              even if it is subsequently reset.
       HOSTNAME
              Automatically set to the name of the current host.
       HOSTTYPE
              Automatically  set  to  a string that uniquely describes the type of machine on which bash is executing.  The default is system-
              dependent.
       LINENO Each time this parameter is referenced, the shell substitutes a decimal number representing the current sequential  line  number
              (starting  with 1) within a script or function.  When not in a script or function, the value substituted is not guaranteed to be
              meaningful.  If LINENO is unset, it loses its special properties, even if it is subsequently reset.
       MACHTYPE
              Automatically set to a string that fully describes the system type on which bash is executing, in the standard GNU  cpu-company-
              system format.  The default is system-dependent.
       MAPFILE
              An array variable (see Arrays below) created to hold the text read by the mapfile builtin when no variable name is supplied.
       OLDPWD The previous working directory as set by the cd command.
       OPTARG The value of the last option argument processed by the getopts builtin command (see SHELL BUILTIN COMMANDS below).
       OPTIND The index of the next argument to be processed by the getopts builtin command (see SHELL BUILTIN COMMANDS below).
       OSTYPE Automatically set to a string that describes the operating system on which bash is executing.  The default is system-dependent.
       PIPESTATUS
              An  array  variable  (see Arrays below) containing a list of exit status values from the processes in the most-recently-executed
              foreground pipeline (which may contain only a single command).
       PPID   The process ID of the shell's parent.  This variable is readonly.
       PWD    The current working directory as set by the cd command.
       RANDOM Each time this parameter is referenced, a random integer between 0 and 32767 is generated.  The sequence of random  numbers  may
              be  initialized by assigning a value to RANDOM.  If RANDOM is unset, it loses its special properties, even if it is subsequently
              reset.
       READLINE_LINE
              The contents of the readline line buffer, for use with "bind -x" (see SHELL BUILTIN COMMANDS below).
       READLINE_POINT
              The position of the insertion point in the readline line buffer, for use with "bind -x" (see SHELL BUILTIN COMMANDS below).
       REPLY  Set to the line of input read by the read builtin command when no arguments are supplied.
       SECONDS
              Each time this parameter is referenced, the number of seconds since shell invocation is returned.  If a  value  is  assigned  to
              SECONDS,  the  value  returned upon subsequent references is the number of seconds since the assignment plus the value assigned.
              If SECONDS is unset, it loses its special properties, even if it is subsequently reset.
       SHELLOPTS
              A colon-separated list of enabled shell options.  Each word in the list is a valid argument for the -o option to the set builtin
              command  (see  SHELL  BUILTIN  COMMANDS below).  The options appearing in SHELLOPTS are those reported as on by set -o.  If this
              variable is in the environment when bash starts up, each shell option in the list will be enabled  before  reading  any  startup
              files.  This variable is read-only.
       SHLVL  Incremented by one each time an instance of bash is started.
       UID    Expands to the user ID of the current user, initialized at shell startup.  This variable is readonly.

       The following variables are used by the shell.  In some cases, bash assigns a default value to a variable; these cases are noted below.

       BASH_ENV
              If  this  parameter  is set when bash is executing a shell script, its value is interpreted as a filename containing commands to
              initialize the shell, as in ~/.bashrc.  The value of BASH_ENV is subjected to parameter  expansion,  command  substitution,  and
              arithmetic expansion before being interpreted as a file name.  PATH is not used to search for the resultant file name.
       BASH_XTRACEFD
              If set to an integer corresponding to a valid file descriptor, bash will write the trace output generated when set -x is enabled
              to that file descriptor.  The file descriptor is closed when  BASH_XTRACEFD  is  unset  or  assigned  a  new  value.   Unsetting
              BASH_XTRACEFD  or  assigning  it  the  empty string causes the trace output to be sent to the standard error.  Note that setting
              BASH_XTRACEFD to 2 (the standard error file descriptor) and then unsetting it will result in the standard error being closed.
       CDPATH The search path for the cd command.  This is a colon-separated list of directories in which  the  shell  looks  for  destination
              directories specified by the cd command.  A sample value is ".:~:/usr".
       COLUMNS
              Used  by  the  select  compound  command  to determine the terminal width when printing selection lists.  Automatically set upon
              receipt of a SIGWINCH.
       COMPREPLY
              An array variable from which bash reads the possible completions generated by a  shell  function  invoked  by  the  programmable
              completion facility (see Programmable Completion below).
       EMACS  If  bash finds this variable in the environment when the shell starts with value "t", it assumes that the shell is running in an
              Emacs shell buffer and disables line editing.
       ENV    Similar to BASH_ENV; used when the shell is invoked in POSIX mode.
       FCEDIT The default editor for the fc builtin command.
       FIGNORE
              A colon-separated list of suffixes to ignore when performing filename completion (see READLINE below).  A filename whose  suffix
              matches  one  of  the  entries  in FIGNORE is excluded from the list of matched filenames.  A sample value is ".o:~" (Quoting is
              needed when assigning a value to this variable, which contains tildes).
       FUNCNEST
              If set to a numeric value greater than 0, defines a maximum function nesting  level.   Function  invocations  that  exceed  this
              nesting level will cause the current command to abort.
       GLOBIGNORE
              A  colon-separated list of patterns defining the set of filenames to be ignored by pathname expansion.  If a filename matched by
              a pathname expansion pattern also matches one of the patterns in GLOBIGNORE, it is removed from the list of matches.
       HISTCONTROL
              A colon-separated list of values controlling how commands are saved on the  history  list.   If  the  list  of  values  includes
              ignorespace,  lines  which  begin  with a space character are not saved in the history list.  A value of ignoredups causes lines
              matching the previous history entry to not be saved.  A value of ignoreboth is shorthand  for  ignorespace  and  ignoredups.   A
              value  of  erasedups causes all previous lines matching the current line to be removed from the history list before that line is
              saved.  Any value not in the above list is ignored.  If HISTCONTROL is unset, or does not include a valid value, all lines  read
              by  the  shell  parser  are saved on the history list, subject to the value of HISTIGNORE.  The second and subsequent lines of a
              multi-line compound command are not tested, and are added to the history regardless of the value of HISTCONTROL.
       HISTFILE
              The name of the file in which command history is saved (see HISTORY below).  The default value is  ~/.bash_history.   If  unset,
              the command history is not saved when an interactive shell exits.
       HISTFILESIZE
              The  maximum  number  of  lines  contained  in  the  history  file.  When this variable is assigned a value, the history file is
              truncated, if necessary, by removing the oldest entries, to contain no more than that number of lines.   The  default  value  is
              500.  The history file is also truncated to this size after writing it when an interactive shell exits.
       HISTIGNORE
              A  colon-separated  list  of  patterns  used to decide which command lines should be saved on the history list.  Each pattern is
              anchored at the beginning of the line and must match the complete line (no implicit `*' is appended).  Each  pattern  is  tested
              against  the  line  after  the  checks  specified  by HISTCONTROL are applied.  In addition to the normal shell pattern matching
              characters, `&' matches the previous history line.  `&' may be escaped using  a  backslash;  the  backslash  is  removed  before
              attempting  a  match.   The  second  and  subsequent lines of a multi-line compound command are not tested, and are added to the
              history regardless of the value of HISTIGNORE.
       HISTSIZE
              The number of commands to remember in the command history (see HISTORY below).  The default value is 500.
       HISTTIMEFORMAT
              If this variable is set and not null, its value is used as a format string for strftime(3) to print the  time  stamp  associated
              with  each history entry displayed by the history builtin.  If this variable is set, time stamps are written to the history file
              so they may be preserved across shell sessions.  This uses the history comment character to distinguish  timestamps  from  other
              history lines.
       HOME   The  home  directory  of  the current user; the default argument for the cd builtin command.  The value of this variable is also
              used when performing tilde expansion.
       HOSTFILE
              Contains the name of a file in the same format as /etc/hosts that should be read when the shell needs to  complete  a  hostname.
              The  list  of  possible  hostname  completions  may  be changed while the shell is running; the next time hostname completion is
              attempted after the value is changed, bash adds the contents of the new file to the existing list.  If HOSTFILE is set, but  has
              no  value,  or  does  not  name  a  readable  file,  bash  attempts  to  read /etc/hosts to obtain the list of possible hostname
              completions.  When HOSTFILE is unset, the hostname list is cleared.
       IFS    The Internal Field Separator that is used for word splitting after expansion and to split lines into words with the read builtin
              command.  The default value is ``<space><tab><newline>''.
       IGNOREEOF
              Controls  the  action of an interactive shell on receipt of an EOF character as the sole input.  If set, the value is the number
              of consecutive EOF characters which must be typed as the first characters on an input line before bash exits.  If  the  variable
              exists but does not have a numeric value, or has no value, the default value is 10.  If it does not exist, EOF signifies the end
              of input to the shell.
       INPUTRC
              The filename for the readline startup file, overriding the default of ~/.inputrc (see READLINE below).
       LANG   Used to determine the locale category for any category not specifically selected with a variable starting with LC_.
       LC_ALL This variable overrides the value of LANG and any other LC_ variable specifying a locale category.
       LC_COLLATE
              This variable determines the collation order used when sorting the results of pathname expansion, and determines the behavior of
              range expressions, equivalence classes, and collating sequences within pathname expansion and pattern matching.
       LC_CTYPE
              This  variable  determines  the interpretation of characters and the behavior of character classes within pathname expansion and
              pattern matching.
       LC_MESSAGES
              This variable determines the locale used to translate double-quoted strings preceded by a $.
       LC_NUMERIC
              This variable determines the locale category used for number formatting.
       LINES  Used by the select compound command to determine the column length for printing selection lists.  Automatically set upon receipt
              of a SIGWINCH.
       MAIL   If  this parameter is set to a file or directory name and the MAILPATH variable is not set, bash informs the user of the arrival
              of mail in the specified file or Maildir-format directory.
       MAILCHECK
              Specifies how often (in seconds) bash checks for mail.  The default is 60 seconds.  When it is time to check for mail, the shell
              does so before displaying the primary prompt.  If this variable is unset, or set to a value that is not a number greater than or
              equal to zero, the shell disables mail checking.
       MAILPATH
              A colon-separated list of file names to be checked for mail.  The message to be printed when mail arrives in a  particular  file
              may  be  specified by separating the file name from the message with a `?'.  When used in the text of the message, $_ expands to
              the name of the current mailfile.  Example:
              MAILPATH='/var/mail/bfox?"You have mail":~/shell-mail?"$_ has mail!"'
              Bash supplies a default value for this variable, but the location of the user mail files that it uses is system dependent (e.g.,
              /var/mail/$USER).
       OPTERR If set to the value 1, bash displays error messages generated by the getopts builtin command (see SHELL BUILTIN COMMANDS below).
              OPTERR is initialized to 1 each time the shell is invoked or a shell script is executed.
       PATH   The search path for commands.  It is a colon-separated list of directories in which the shell looks for  commands  (see  COMMAND
              EXECUTION  below).   A zero-length (null) directory name in the value of PATH indicates the current directory.  A null directory
              name may appear as two adjacent colons, or as an initial or trailing colon.  The default path is system-dependent, and is set by
              the administrator who installs bash.  A common value is ``/usr/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin''.
       POSIXLY_CORRECT
              If this variable is in the environment when bash starts, the shell enters posix mode before reading the startup files, as if the
              --posix invocation option had been supplied.  If it is set while the shell is running,  bash  enables  posix  mode,  as  if  the
              command set -o posix had been executed.
       PROMPT_COMMAND
              If set, the value is executed as a command prior to issuing each primary prompt.
       PROMPT_DIRTRIM
              If  set to a number greater than zero, the value is used as the number of trailing directory components to retain when expanding
              the \w and \W prompt string escapes (see PROMPTING below).  Characters removed are replaced with an ellipsis.
       PS1    The value of this parameter is expanded (see PROMPTING below) and used as the primary  prompt  string.   The  default  value  is
              ``\s-\v\$ ''.
       PS2    The value of this parameter is expanded as with PS1 and used as the secondary prompt string.  The default is ``> ''.
       PS3    The value of this parameter is used as the prompt for the select command (see SHELL GRAMMAR above).
       PS4    The  value  of  this  parameter  is  expanded  as  with PS1 and the value is printed before each command bash displays during an
              execution trace.  The first character of PS4 is replicated  multiple  times,  as  necessary,  to  indicate  multiple  levels  of
              indirection.  The default is ``+ ''.
       SHELL  The full pathname to the shell is kept in this environment variable.  If it is not set when the shell starts, bash assigns to it
              the full pathname of the current user's login shell.
       TIMEFORMAT
              The value of this parameter is used as a format string specifying how the timing information for  pipelines  prefixed  with  the
              time reserved word should be displayed.  The % character introduces an escape sequence that is expanded to a time value or other
              information.  The escape sequences and their meanings are as follows; the braces denote optional portions.
              %%        A literal %.
              %[p][l]R  The elapsed time in seconds.
              %[p][l]U  The number of CPU seconds spent in user mode.
              %[p][l]S  The number of CPU seconds spent in system mode.
              %P        The CPU percentage, computed as (%U + %S) / %R.

              The optional p is a digit specifying the precision, the number of fractional digits after a decimal point.  A value of 0  causes
              no  decimal  point or fraction to be output.  At most three places after the decimal point may be specified; values of p greater
              than 3 are changed to 3.  If p is not specified, the value 3 is used.

              The optional l specifies a longer format, including minutes, of the form MMmSS.FFs.  The value of p determines  whether  or  not
              the fraction is included.

              If  this  variable  is not set, bash acts as if it had the value $'\nreal\t%3lR\nuser\t%3lU\nsys%3lS'.  If the value is null, no
              timing information is displayed.  A trailing newline is added when the format string is displayed.
       TMOUT  If set to a value greater than zero, TMOUT is treated as  the  default  timeout  for  the  read  builtin.   The  select  command
              terminates  if  input  does  not  arrive after TMOUT seconds when input is coming from a terminal.  In an interactive shell, the
              value is interpreted as the number of seconds to wait for input after issuing the primary prompt.  Bash terminates after waiting
              for that number of seconds if input does not arrive.
       TMPDIR If set, bash uses its value as the name of a directory in which bash creates temporary files for the shell's use.
       auto_resume
              This  variable  controls  how  the  shell  interacts with the user and job control.  If this variable is set, single word simple
              commands without redirections are treated as candidates for resumption of an  existing  stopped  job.   There  is  no  ambiguity
              allowed; if there is more than one job beginning with the string typed, the job most recently accessed is selected.  The name of
              a stopped job, in this context, is the command line used to start it.  If set to the value exact, the string supplied must match
              the  name of a stopped job exactly; if set to substring, the string supplied needs to match a substring of the name of a stopped
              job.  The substring value provides functionality analogous to the %?  job identifier (see JOB CONTROL below).   If  set  to  any
              other  value, the supplied string must be a prefix of a stopped job's name; this provides functionality analogous to the %string
              job identifier.
       histchars
              The two or three characters which control history expansion and tokenization (see HISTORY EXPANSION below).  The first character
              is  the  history  expansion  character,  the character which signals the start of a history expansion, normally `!'.  The second
              character is the quick substitution character, which  is  used  as  shorthand  for  re-running  the  previous  command  entered,
              substituting  one  string  for another in the command.  The default is `^'.  The optional third character is the character which
              indicates that the remainder of the line is a comment when found as the first character of a word, normally  `#'.   The  history
              comment  character causes history substitution to be skipped for the remaining words on the line.  It does not necessarily cause
              the shell parser to treat the rest of the line as a comment.

   Arrays
       Bash provides one-dimensional indexed and associative array variables.  Any variable may be used  as  an  indexed  array;  the  declare
       builtin  will  explicitly  declare  an  array.   There is no maximum limit on the size of an array, nor any requirement that members be
       indexed or assigned contiguously.  Indexed arrays are referenced using integers (including arithmetic expressions)  and are zero-based;
       associative arrays are referenced using arbitrary strings.

       An  indexed  array  is  created  automatically if any variable is assigned to using the syntax name[subscript]=value.  The subscript is
       treated as an arithmetic expression that must evaluate to a number.  If subscript evaluates to a number less than zero, it is  used  as
       an offset from one greater than the array's maximum index (so a subcript of -1 refers to the last element of the array).  To explicitly
       declare an indexed array, use declare -a name (see SHELL BUILTIN COMMANDS below).  declare -a name[subscript]  is  also  accepted;  the
       subscript is ignored.

       Associative arrays are created using declare -A name.

       Attributes may be specified for an array variable using the declare and readonly builtins.  Each attribute applies to all members of an
       array.

       Arrays are assigned to  using  compound  assignments  of  the  form  name=(value1  ...  valuen),  where  each  value  is  of  the  form
       [subscript]=string.   Indexed  array  assignments  do  not require the bracket and subscript.  When assigning to indexed arrays, if the
       optional brackets and subscript are supplied, that index is assigned to; otherwise the index of the element assigned is the last  index
       assigned to by the statement plus one.  Indexing starts at zero.

       When assigning to an associative array, the subscript is required.

       This  syntax  is  also  accepted  by the declare builtin.  Individual array elements may be assigned to using the name[subscript]=value
       syntax introduced above.

       Any element of an array may be referenced using  ${name[subscript]}.   The  braces  are  required  to  avoid  conflicts  with  pathname
       expansion.  If subscript is @ or *, the word expands to all members of name.  These subscripts differ only when the word appears within
       double quotes.  If the word is double-quoted, ${name[*]} expands to a single word with the value of each array member separated by  the
       first  character  of the IFS special variable, and ${name[@]} expands each element of name to a separate word.  When there are no array
       members, ${name[@]} expands to nothing.  If the double-quoted expansion occurs within a word, the expansion of the first  parameter  is
       joined  with  the  beginning  part  of  the  original word, and the expansion of the last parameter is joined with the last part of the
       original  word.   This  is  analogous  to  the  expansion  of  the  special  parameters  *  and  @  (see  Special  Parameters   above).
       ${#name[subscript]}  expands  to  the length of ${name[subscript]}.  If subscript is * or @, the expansion is the number of elements in
       the array.  Referencing an array variable without a subscript is equivalent to referencing the array with a subscript of 0.

       An array variable is considered set if a subscript has been assigned a value.  The null string is a valid value.

       The unset builtin is used to destroy arrays.  unset name[subscript] destroys the array element at index subscript.  Care must be  taken
       to  avoid  unwanted  side  effects  caused  by pathname expansion.  unset name, where name is an array, or unset name[subscript], where
       subscript is * or @, removes the entire array.

       The declare, local, and readonly builtins each accept a -a option to specify an indexed array and a -A option to specify an associative
       array.   If  both  options are supplied, -A takes precedence.  The read builtin accepts a -a option to assign a list of words read from
       the standard input to an array.  The set and declare builtins display array  values  in  a  way  that  allows  them  to  be  reused  as
       assignments.

EXPANSION

       Expansion  is  performed  on  the command line after it has been split into words.  There are seven kinds of expansion performed: brace
       expansion, tilde expansion, parameter and variable expansion, command substitution, arithmetic expansion, word splitting, and  pathname
       expansion.

       The  order  of  expansions  is: brace expansion, tilde expansion, parameter, variable and arithmetic expansion and command substitution
       (done in a left-to-right fashion), word splitting, and pathname expansion.

       On systems that can support it, there is an additional expansion available: process substitution.

       Only brace expansion, word splitting, and pathname expansion can change the number of words of the expansion; other expansions expand a
       single  word  to  a  single  word.   The  only  exceptions  to this are the expansions of "$@" and "${name[@]}" as explained above (see
       PARAMETERS).

   Brace Expansion
       Brace expansion is a mechanism by which arbitrary strings may be generated.  This mechanism is similar to pathname expansion,  but  the
       filenames  generated  need not exist.  Patterns to be brace expanded take the form of an optional preamble, followed by either a series
       of comma-separated strings or a sequence expression between a pair of braces, followed by an  optional  postscript.   The  preamble  is
       prefixed  to  each  string contained within the braces, and the postscript is then appended to each resulting string, expanding left to
       right.

       Brace expansions may be nested.  The results of each expanded string are not sorted; left to right order is  preserved.   For  example,
       a{d,c,b}e expands into `ade ace abe'.

       A  sequence  expression  takes  the  form {x..y[..incr]}, where x and y are either integers or single characters, and incr, an optional
       increment, is an integer.  When integers are supplied, the expression expands to each number between  x  and  y,  inclusive.   Supplied
       integers  may  be prefixed with 0 to force each term to have the same width.  When either x or y begins with a zero, the shell attempts
       to force all generated terms to contain the same number of digits, zero-padding where necessary.  When  characters  are  supplied,  the
       expression  expands  to  each character lexicographically between x and y, inclusive.  Note that both x and y must be of the same type.
       When the increment is supplied, it is used as the difference between each term.  The default increment is 1 or -1 as appropriate.

       Brace expansion is performed before any other expansions, and any characters special to other expansions are preserved in  the  result.
       It  is  strictly  textual.   Bash  does  not apply any syntactic interpretation to the context of the expansion or the text between the
       braces.

       A correctly-formed brace expansion must contain unquoted opening and closing braces, and  at  least  one  unquoted  comma  or  a  valid
       sequence expression.  Any incorrectly formed brace expansion is left unchanged.  A { or , may be quoted with a backslash to prevent its
       being considered part of a brace expression.  To avoid conflicts with parameter expansion, the string ${ is not considered eligible for
       brace expansion.

       This  construct  is  typically  used  as  shorthand  when  the common prefix of the strings to be generated is longer than in the above
       example:

              mkdir /usr/local/src/bash/{old,new,dist,bugs}
       or
              chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}

       Brace expansion introduces a slight incompatibility with historical versions of sh.  sh  does  not  treat  opening  or  closing  braces
       specially  when  they  appear  as part of a word, and preserves them in the output.  Bash removes braces from words as a consequence of
       brace expansion.  For example, a word entered to sh as file{1,2} appears identically in the output.  The same word is output  as  file1
       file2  after  expansion  by bash.  If strict compatibility with sh is desired, start bash with the +B option or disable brace expansion
       with the +B option to the set command (see SHELL BUILTIN COMMANDS below).

   Tilde Expansion
       If a word begins with an unquoted tilde character (`~'), all of the characters preceding the first unquoted slash (or  all  characters,
       if there is no unquoted slash) are considered a tilde-prefix.  If none of the characters in the tilde-prefix are quoted, the characters
       in the tilde-prefix following the tilde are treated as a possible login name.  If this login name is the  null  string,  the  tilde  is
       replaced  with  the  value  of  the  shell  parameter  HOME.   If  HOME is unset, the home directory of the user executing the shell is
       substituted instead.  Otherwise, the tilde-prefix is replaced with the home directory associated with the specified login name.

       If the tilde-prefix is a `~+', the value of the shell variable PWD replaces the tilde-prefix.  If the tilde-prefix is a `~-', the value
       of  the  shell  variable  OLDPWD, if it is set, is substituted.  If the characters following the tilde in the tilde-prefix consist of a
       number N, optionally prefixed by a `+' or a `-', the tilde-prefix is replaced with the corresponding element from the directory  stack,
       as  it  would  be displayed by the dirs builtin invoked with the tilde-prefix as an argument.  If the characters following the tilde in
       the tilde-prefix consist of a number without a leading `+' or `-', `+' is assumed.

       If the login name is invalid, or the tilde expansion fails, the word is unchanged.

       Each variable assignment is checked for unquoted tilde-prefixes immediately following a : or  the  first  =.   In  these  cases,  tilde
       expansion  is  also  performed.  Consequently, one may use file names with tildes in assignments to PATH, MAILPATH, and CDPATH, and the
       shell assigns the expanded value.

   Parameter Expansion
       The `$' character introduces parameter expansion, command substitution, or arithmetic expansion.  The parameter name or  symbol  to  be
       expanded  may  be  enclosed  in braces, which are optional but serve to protect the variable to be expanded from characters immediately
       following it which could be interpreted as part of the name.

       When braces are used, the matching ending brace is the first `}' not escaped by a backslash or within a quoted string, and  not  within
       an embedded arithmetic expansion, command substitution, or parameter expansion.

       ${parameter}
              The  value  of  parameter  is  substituted.  The braces are required when parameter is a positional parameter with more than one
              digit, or when parameter is followed by a character which is not to be interpreted as part of its name.

       If the first character of parameter is an exclamation point (!), a level of variable indirection is introduced.  Bash uses the value of
       the  variable  formed  from the rest of parameter as the name of the variable; this variable is then expanded and that value is used in
       the rest of the substitution, rather than the value of parameter itself.  This is known as indirect expansion.  The exceptions to  this
       are  the  expansions  of  ${!prefix*} and ${!name[@]} described below.  The exclamation point must immediately follow the left brace in
       order to introduce indirection.

       In each of the cases below, word is subject to tilde expansion, parameter expansion, command substitution, and arithmetic expansion.

       When not performing substring expansion, using the forms documented below, bash tests for a parameter that is unset or null.   Omitting
       the colon results in a test only for a parameter that is unset.

       ${parameter:-word}
              Use  Default Values.  If parameter is unset or null, the expansion of word is substituted.  Otherwise, the value of parameter is
              substituted.
       ${parameter:=word}
              Assign Default Values.  If parameter is unset or null, the expansion of word is assigned to parameter.  The value  of  parameter
              is then substituted.  Positional parameters and special parameters may not be assigned to in this way.
       ${parameter:?word}
              Display  Error  if  Null or Unset.  If parameter is null or unset, the expansion of word (or a message to that effect if word is
              not present) is written to the standard error and the shell, if it is not interactive, exits.  Otherwise, the value of parameter
              is substituted.
       ${parameter:+word}
              Use Alternate Value.  If parameter is null or unset, nothing is substituted, otherwise the expansion of word is substituted.
       ${parameter:offset}
       ${parameter:offset:length}
              Substring  Expansion.  Expands to up to length characters of parameter starting at the character specified by offset.  If length
              is omitted, expands to the substring of parameter starting at  the  character  specified  by  offset.   length  and  offset  are
              arithmetic  expressions (see ARITHMETIC EVALUATION below).  If offset evaluates to a number less than zero, the value is used as
              an offset from the end of the value of parameter.  Arithmetic expressions starting with a - must be separated by whitespace from
              the  preceding : to be distinguished from the Use Default Values expansion.  If length evaluates to a number less than zero, and
              parameter is not @ and not an indexed or associative array, it is interpreted as  an  offset  from  the  end  of  the  value  of
              parameter  rather  than a number of characters, and the expansion is the characters between the two offsets.  If parameter is @,
              the result is length positional parameters beginning at offset.  If parameter is an indexed array name subscripted by  @  or  *,
              the  result  is the length members of the array beginning with ${parameter[offset]}.  A negative offset is taken relative to one
              greater than the maximum index of the specified array.  Substring expansion applied to an associative array  produces  undefined
              results.  Note that a negative offset must be separated from the colon by at least one space to avoid being confused with the :-
              expansion.  Substring indexing is zero-based unless the positional parameters are used, in which case the indexing starts  at  1
              by default.  If offset is 0, and the positional parameters are used, $0 is prefixed to the list.

       ${!prefix*}
       ${!prefix@}
              Names matching prefix.  Expands to the names of variables whose names begin with prefix, separated by the first character of the
              IFS special variable.  When @ is used and the expansion appears within double quotes, each variable name expands to  a  separate
              word.

       ${!name[@]}
       ${!name[*]}
              List of array keys.  If name is an array variable, expands to the list of array indices (keys) assigned in name.  If name is not
              an array, expands to 0 if name is set and null otherwise.  When @ is used and the expansion appears within double  quotes,  each
              key expands to a separate word.

       ${#parameter}
              Parameter  length.   The  length  in  characters  of  the  value of parameter is substituted.  If parameter is * or @, the value
              substituted is the number of positional parameters.  If parameter is an array name subscripted by * or @, the value  substituted
              is the number of elements in the array.

       ${parameter#word}
       ${parameter##word}
              Remove  matching  prefix  pattern.   The  word  is  expanded to produce a pattern just as in pathname expansion.  If the pattern
              matches the beginning of the value of parameter, then the result of the expansion is the expanded value of  parameter  with  the
              shortest  matching  pattern (the ``#'' case) or the longest matching pattern (the ``##'' case) deleted.  If parameter is @ or *,
              the pattern removal operation is applied to each positional parameter in turn, and the expansion  is  the  resultant  list.   If
              parameter  is an array variable subscripted with @ or *, the pattern removal operation is applied to each member of the array in
              turn, and the expansion is the resultant list.

       ${parameter%word}
       ${parameter%%word}
              Remove matching suffix pattern.  The word is expanded to produce a pattern just  as  in  pathname  expansion.   If  the  pattern
              matches  a  trailing  portion  of  the  expanded  value  of parameter, then the result of the expansion is the expanded value of
              parameter with the shortest matching pattern (the ``%'' case) or the longest matching pattern (the  ``%%''  case)  deleted.   If
              parameter  is  @  or  *, the pattern removal operation is applied to each positional parameter in turn, and the expansion is the
              resultant list.  If parameter is an array variable subscripted with @ or *, the pattern removal operation  is  applied  to  each
              member of the array in turn, and the expansion is the resultant list.

       ${parameter/pattern/string}
              Pattern  substitution.   The  pattern is expanded to produce a pattern just as in pathname expansion.  Parameter is expanded and
              the longest match of pattern against its value is replaced with string.  If pattern begins with /, all matches  of  pattern  are
              replaced  with  string.  Normally only the first match is replaced.  If pattern begins with #, it must match at the beginning of
              the expanded value of parameter.  If pattern begins with %, it must match at the end of the expanded  value  of  parameter.   If
              string  is  null,  matches  of  pattern  are  deleted  and  the / following pattern may be omitted.  If parameter is @ or *, the
              substitution operation is applied to each positional parameter in turn, and the expansion is the resultant list.   If  parameter
              is an array variable subscripted with @ or *, the substitution operation is applied to each member of the array in turn, and the
              expansion is the resultant list.

       ${parameter^pattern}
       ${parameter^^pattern}
       ${parameter,pattern}
       ${parameter,,pattern}
              Case modification.  This expansion modifies the case of alphabetic characters in parameter.  The pattern is expanded to  produce
              a  pattern  just  as  in  pathname  expansion.   The  ^ operator converts lowercase letters matching pattern to uppercase; the ,
              operator converts matching uppercase letters to lowercase.  The ^^ and ,, expansions  convert  each  matched  character  in  the
              expanded value; the ^ and , expansions match and convert only the first character in the expanded value.  If pattern is omitted,
              it is treated like a ?, which matches every character.  If parameter is @ or *, the case modification operation  is  applied  to
              each  positional parameter in turn, and the expansion is the resultant list.  If parameter is an array variable subscripted with
              @ or *, the case modification operation is applied to each member of the array in turn, and the expansion is the resultant list.

   Command Substitution
       Command substitution allows the output of a command to replace the command name.  There are two forms:

              $(command)
       or
              `command`

       Bash performs the expansion by executing command and replacing the command substitution with the standard output of the  command,  with
       any  trailing  newlines  deleted.   Embedded  newlines  are  not  deleted,  but they may be removed during word splitting.  The command
       substitution $(cat file) can be replaced by the equivalent but faster $(< file).

       When the old-style backquote form of substitution is used, backslash retains its literal meaning except when followed by $,  `,  or  \.
       The  first  backquote  not preceded by a backslash terminates the command substitution.  When using the $(command) form, all characters
       between the parentheses make up the command; none are treated specially.

       Command substitutions may be nested.  To nest when using the backquoted form, escape the inner backquotes with backslashes.

       If the substitution appears within double quotes, word splitting and pathname expansion are not performed on the results.

   Arithmetic Expansion
       Arithmetic expansion allows the evaluation of an arithmetic expression and the substitution of the result.  The format  for  arithmetic
       expansion is:

              $((expression))

       The old format $[expression] is deprecated and will be removed in upcoming versions of bash.

       The  expression is treated as if it were within double quotes, but a double quote inside the parentheses is not treated specially.  All
       tokens in the expression undergo parameter expansion, string expansion, command substitution, and quote removal.  Arithmetic expansions
       may be nested.

       The  evaluation  is performed according to the rules listed below under ARITHMETIC EVALUATION.  If expression is invalid, bash prints a
       message indicating failure and no substitution occurs.

   Process Substitution
       Process substitution is supported on systems that support named pipes (FIFOs) or the /dev/fd method of naming open files.  It takes the
       form of <(list) or >(list).  The process list is run with its input or output connected to a FIFO or some file in /dev/fd.  The name of
       this file is passed as an argument to the current command as the result of the expansion.  If the >(list) form is used, writing to  the
       file  will  provide input for list.  If the <(list) form is used, the file passed as an argument should be read to obtain the output of
       list.

       When available, process substitution is performed simultaneously with parameter  and  variable  expansion,  command  substitution,  and
       arithmetic expansion.

   Word Splitting
       The  shell  scans  the  results of parameter expansion, command substitution, and arithmetic expansion that did not occur within double
       quotes for word splitting.

       The shell treats each character of IFS as a delimiter, and splits the results of the other expansions into words on  these  characters.
       If  IFS  is  unset,  or its value is exactly <space><tab><newline>, the default, then sequences of <space>, <tab>, and <newline> at the
       beginning and end of the results of the previous expansions are ignored, and any sequence of IFS characters not at the beginning or end
       serves  to  delimit  words.   If  IFS has a value other than the default, then sequences of the whitespace characters space and tab are
       ignored at the beginning and end of the word, as long as the whitespace character is in the value of IFS (an IFS whitespace character).
       Any  character  in  IFS that is not IFS whitespace, along with any adjacent IFS whitespace characters, delimits a field.  A sequence of
       IFS whitespace characters is also treated as a delimiter.  If the value of IFS is null, no word splitting occurs.

       Explicit null arguments ("" or '') are retained.  Unquoted implicit null arguments, resulting from the  expansion  of  parameters  that
       have no values, are removed.  If a parameter with no value is expanded within double quotes, a null argument results and is retained.

       Note that if no expansion occurs, no splitting is performed.

   Pathname Expansion
       After  word  splitting,  unless  the  -f  option  has  been  set, bash scans each word for the characters *, ?, and [.  If one of these
       characters appears, then the word is regarded as a pattern, and replaced with an alphabetically sorted list of file names matching  the
       pattern.   If  no  matching  file  names  are  found, and the shell option nullglob is not enabled, the word is left unchanged.  If the
       nullglob option is set, and no matches are found, the word is removed.  If the failglob shell option is set, and no matches are  found,
       an error message is printed and the command is not executed.  If the shell option nocaseglob is enabled, the match is performed without
       regard to the case of alphabetic characters.  Note that when using range expressions like [a-z] (see below), letters of the other  case
       may  be  included,  depending on the setting of LC_COLLATE.  When a pattern is used for pathname expansion, the character ``.''  at the
       start of a name or immediately following a slash must be matched explicitly, unless the shell option dotglob is set.  When  matching  a
       pathname,  the  slash character must always be matched explicitly.  In other cases, the ``.''  character is not treated specially.  See
       the description of shopt below under SHELL BUILTIN COMMANDS for a description of the nocaseglob, nullglob, failglob, and dotglob  shell
       options.

       The  GLOBIGNORE  shell  variable may be used to restrict the set of file names matching a pattern.  If GLOBIGNORE is set, each matching
       file name that also matches one of the patterns in GLOBIGNORE is removed from the list of matches.  The file names  ``.''   and  ``..''
       are always ignored when GLOBIGNORE is set and not null.  However, setting GLOBIGNORE to a non-null value has the effect of enabling the
       dotglob shell option, so all other file names beginning with a ``.''  will match.  To get the  old  behavior  of  ignoring  file  names
       beginning with a ``.'', make ``.*''  one of the patterns in GLOBIGNORE.  The dotglob option is disabled when GLOBIGNORE is unset.

       Pattern Matching

       Any  character that appears in a pattern, other than the special pattern characters described below, matches itself.  The NUL character
       may not occur in a pattern.  A backslash escapes the following character; the escaping  backslash  is  discarded  when  matching.   The
       special pattern characters must be quoted if they are to be matched literally.

       The special pattern characters have the following meanings:

              *      Matches  any  string,  including the null string.  When the globstar shell option is enabled, and * is used in a pathname
                     expansion context, two adjacent *s used as a single pattern will match  all  files  and  zero  or  more  directories  and
                     subdirectories.  If followed by a /, two adjacent *s will match only directories and subdirectories.
              ?      Matches any single character.
              [...]  Matches  any  one of the enclosed characters.  A pair of characters separated by a hyphen denotes a range expression; any
                     character that sorts between those two characters, inclusive, using the current locale's collating sequence and character
                     set,  is matched.  If the first character following the [ is a !  or a ^ then any character not enclosed is matched.  The
                     sorting order of characters in range expressions is determined by the current locale and  the  value  of  the  LC_COLLATE
                     shell  variable,  if  set.   A  -  may  be matched by including it as the first or last character in the set.  A ] may be
                     matched by including it as the first character in the set.

                     Within [ and ], character classes can be specified using the syntax [:class:],  where  class  is  one  of  the  following
                     classes defined in the POSIX standard:
                     alnum alpha ascii blank cntrl digit graph lower print punct space upper word xdigit
                     A  character  class matches any character belonging to that class.  The word character class matches letters, digits, and
                     the character _.

                     Within [ and ], an equivalence class can be specified using the syntax [=c=], which matches all characters with the  same
                     collation weight (as defined by the current locale) as the character c.

                     Within [ and ], the syntax [.symbol.] matches the collating symbol symbol.

       If  the  extglob  shell  option is enabled using the shopt builtin, several extended pattern matching operators are recognized.  In the
       following description, a pattern-list is a list of one or more patterns separated by a |.  Composite patterns may be formed  using  one
       or more of the following sub-patterns:

              ?(pattern-list)
                     Matches zero or one occurrence of the given patterns
              *(pattern-list)
                     Matches zero or more occurrences of the given patterns
              +(pattern-list)
                     Matches one or more occurrences of the given patterns
              @(pattern-list)
                     Matches one of the given patterns
              !(pattern-list)
                     Matches anything except one of the given patterns

   Quote Removal
       After  the  preceding  expansions,  all  unquoted  occurrences  of the characters \, ', and " that did not result from one of the above
       expansions are removed.

REDIRECTION

       Before a command is executed, its input and output may be redirected using a special notation interpreted by  the  shell.   Redirection
       may  also be used to open and close files for the current shell execution environment.  The following redirection operators may precede
       or appear anywhere within a simple command or may follow a command.  Redirections are processed in the order they appear, from left  to
       right.

       Each  redirection  that  may  be preceded by a file descriptor number may instead be preceded by a word of the form {varname}.  In this
       case, for each redirection operator except >&- and <&-, the shell will allocate a file descriptor greater than  10  and  assign  it  to
       varname.  If >&- or <&- is preceded by {varname}, the value of varname defines the file descriptor to close.

       In  the following descriptions, if the file descriptor number is omitted, and the first character of the redirection operator is <, the
       redirection refers to the standard input (file descriptor 0).  If the first character of the redirection operator is >, the redirection
       refers to the standard output (file descriptor 1).

       The  word  following  the  redirection operator in the following descriptions, unless otherwise noted, is subjected to brace expansion,
       tilde expansion, parameter expansion,  command  substitution,  arithmetic  expansion,  quote  removal,  pathname  expansion,  and  word
       splitting.  If it expands to more than one word, bash reports an error.

       Note that the order of redirections is significant.  For example, the command

              ls > dirlist 2>&1

       directs both standard output and standard error to the file dirlist, while the command

              ls 2>&1 > dirlist

       directs  only  the  standard  output  to  file  dirlist,  because the standard error was duplicated from the standard output before the
       standard output was redirected to dirlist.

       Bash handles several filenames specially when they are used in redirections, as described in the following table:

              /dev/fd/fd
                     If fd is a valid integer, file descriptor fd is duplicated.
              /dev/stdin
                     File descriptor 0 is duplicated.
              /dev/stdout
                     File descriptor 1 is duplicated.
              /dev/stderr
                     File descriptor 2 is duplicated.
              /dev/tcp/host/port
                     If host is a valid hostname or Internet address, and port is an integer port number or service  name,  bash  attempts  to
                     open a TCP connection to the corresponding socket.
              /dev/udp/host/port
                     If  host  is  a  valid hostname or Internet address, and port is an integer port number or service name, bash attempts to
                     open a UDP connection to the corresponding socket.

       A failure to open or create a file causes the redirection to fail.

       Redirections using file descriptors greater than 9 should be used with care, as they may conflict with file descriptors the shell  uses
       internally.

       Note that the exec builtin command can make redirections take effect in the current shell.

   Redirecting Input
       Redirection  of  input  causes the file whose name results from the expansion of word to be opened for reading on file descriptor n, or
       the standard input (file descriptor 0) if n is not specified.

       The general format for redirecting input is:

              [n]<word

   Redirecting Output
       Redirection of output causes the file whose name results from the expansion of word to be opened for writing on file descriptor  n,  or
       the  standard  output  (file  descriptor  1)  if  n is not specified.  If the file does not exist it is created; if it does exist it is
       truncated to zero size.

       The general format for redirecting output is:

              [n]>word

       If the redirection operator is >, and the noclobber option to the set builtin has been enabled, the redirection will fail if  the  file
       whose  name  results  from  the  expansion of word exists and is a regular file.  If the redirection operator is >|, or the redirection
       operator is > and the noclobber option to the set builtin command is not enabled, the redirection is attempted even if the  file  named
       by word exists.

   Appending Redirected Output
       Redirection  of output in this fashion causes the file whose name results from the expansion of word to be opened for appending on file
       descriptor n, or the standard output (file descriptor 1) if n is not specified.  If the file does not exist it is created.

       The general format for appending output is:

              [n]>>word

   Redirecting Standard Output and Standard Error
       This construct allows both the standard output (file descriptor 1) and the standard error output (file descriptor 2) to  be  redirected
       to the file whose name is the expansion of word.

       There are two formats for redirecting standard output and standard error:

              &>word
       and
              >&word

       Of the two forms, the first is preferred.  This is semantically equivalent to

              >word 2>&1

   Appending Standard Output and Standard Error
       This  construct allows both the standard output (file descriptor 1) and the standard error output (file descriptor 2) to be appended to
       the file whose name is the expansion of word.

       The format for appending standard output and standard error is:

              &>>word

       This is semantically equivalent to

              >>word 2>&1

   Here Documents
       This type of redirection instructs the shell to read input from the current source until a line  containing  only  delimiter  (with  no
       trailing blanks) is seen.  All of the lines read up to that point are then used as the standard input for a command.

       The format of here-documents is:

              <<[-]word
                      here-document
              delimiter

       No  parameter  expansion, command substitution, arithmetic expansion, or pathname expansion is performed on word.  If any characters in
       word are quoted, the delimiter is the result of quote removal on word, and the lines in the here-document are not expanded.  If word is
       unquoted,  all lines of the here-document are subjected to parameter expansion, command substitution, and arithmetic expansion.  In the
       latter case, the character sequence \<newline> is ignored, and \ must be used to quote the characters \, $, and `.

       If the redirection operator is <<-, then all leading tab characters are stripped from input lines and the  line  containing  delimiter.
       This allows here-documents within shell scripts to be indented in a natural fashion.

   Here Strings
       A variant of here documents, the format is:

              <<<word

       The word is expanded and supplied to the command on its standard input.

   Duplicating File Descriptors
       The redirection operator

              [n]<&word

       is  used  to duplicate input file descriptors.  If word expands to one or more digits, the file descriptor denoted by n is made to be a
       copy of that file descriptor.  If the digits in word do not specify a file descriptor open for input, a redirection error  occurs.   If
       word evaluates to -, file descriptor n is closed.  If n is not specified, the standard input (file descriptor 0) is used.

       The operator

              [n]>&word

       is  used  similarly  to duplicate output file descriptors.  If n is not specified, the standard output (file descriptor 1) is used.  If
       the digits in word do not specify a file descriptor open for output, a redirection error occurs.  As a special case, if n  is  omitted,
       and word does not expand to one or more digits, the standard output and standard error are redirected as described previously.

   Moving File Descriptors
       The redirection operator

              [n]<&digit-

       moves the file descriptor digit to file descriptor n, or the standard input (file descriptor 0) if n is not specified.  digit is closed
       after being duplicated to n.

       Similarly, the redirection operator

              [n]>&digit-

       moves the file descriptor digit to file descriptor n, or the standard output (file descriptor 1) if n is not specified.

   Opening File Descriptors for Reading and Writing
       The redirection operator

              [n]<>word

       causes the file whose name is the expansion of word to be opened for both reading  and  writing  on  file  descriptor  n,  or  on  file
       descriptor 0 if n is not specified.  If the file does not exist, it is created.

ALIASES

       Aliases  allow a string to be substituted for a word when it is used as the first word of a simple command.  The shell maintains a list
       of aliases that may be set and unset with the alias and unalias builtin commands (see SHELL BUILTIN COMMANDS below).  The first word of
       each  simple  command,  if unquoted, is checked to see if it has an alias.  If so, that word is replaced by the text of the alias.  The
       characters /, $, `, and = and any of the shell metacharacters or quoting characters listed above may not appear in an alias name.   The
       replacement  text  may contain any valid shell input, including shell metacharacters.  The first word of the replacement text is tested
       for aliases, but a word that is identical to an alias being expanded is not expanded a second time.  This means that one may  alias  ls
       to  ls -F, for instance, and bash does not try to recursively expand the replacement text.  If the last character of the alias value is
       a blank, then the next command word following the alias is also checked for alias expansion.

       Aliases are created and listed with the alias command, and removed with the unalias command.

       There is no mechanism for using arguments in the replacement text.  If arguments are needed, a  shell  function  should  be  used  (see
       FUNCTIONS below).

       Aliases  are  not  expanded  when  the  shell  is  not  interactive, unless the expand_aliases shell option is set using shopt (see the
       description of shopt under SHELL BUILTIN COMMANDS below).

       The rules concerning the definition and use of aliases are somewhat confusing.  Bash always reads at least one complete line  of  input
       before  executing  any of the commands on that line.  Aliases are expanded when a command is read, not when it is executed.  Therefore,
       an alias definition appearing on the same line as another command does not take effect until the next  line  of  input  is  read.   The
       commands  following the alias definition on that line are not affected by the new alias.  This behavior is also an issue when functions
       are executed.  Aliases are expanded when a function definition is  read,  not  when  the  function  is  executed,  because  a  function
       definition  is  itself a compound command.  As a consequence, aliases defined in a function are not available until after that function
       is executed.  To be safe, always put alias definitions on a separate line, and do not use alias in compound commands.

       For almost every purpose, aliases are superseded by shell functions.

FUNCTIONS

       A shell function, defined as described above under SHELL GRAMMAR, stores a series of commands for later execution.  When the name of  a
       shell  function  is  used as a simple command name, the list of commands associated with that function name is executed.  Functions are
       executed in the context of the current shell; no new process is created to interpret them (contrast this with the execution of a  shell
       script).   When  a  function  is  executed,  the  arguments to the function become the positional parameters during its execution.  The
       special parameter # is updated to reflect the change.  Special parameter 0 is unchanged.  The first element of the FUNCNAME variable is
       set to the name of the function while the function is executing.

       All  other aspects of the shell execution environment are identical between a function and its caller with these exceptions:  the DEBUG
       and RETURN traps (see the description of the trap builtin under SHELL BUILTIN COMMANDS below) are not inherited unless the function has
       been  given  the  trace  attribute (see the description of the declare builtin below) or the -o functrace shell option has been enabled
       with the set builtin (in which case all functions inherit the DEBUG and RETURN traps), and the ERR trap is not inherited unless the  -o
       errtrace shell option has been enabled.

       Variables  local  to  the  function  may be declared with the local builtin command.  Ordinarily, variables and their values are shared
       between the function and its caller.

       The FUNCNEST variable, if set to a numeric value greater than 0, defines a maximum function nesting level.  Function  invocations  that
       exceed the limit cause the entire command to abort.

       If  the  builtin command return is executed in a function, the function completes and execution resumes with the next command after the
       function call.  Any command associated with the RETURN trap is executed before execution  resumes.   When  a  function  completes,  the
       values of the positional parameters and the special parameter # are restored to the values they had prior to the function's execution.

       Function  names  and definitions may be listed with the -f option to the declare or typeset builtin commands.  The -F option to declare
       or typeset will list the function names only (and optionally the source file and line number, if the extdebug shell option is enabled).
       Functions  may  be  exported  so  that  subshells automatically have them defined with the -f option to the export builtin.  A function
       definition may be deleted using the -f option to the unset builtin.  Note that shell functions and variables with  the  same  name  may
       result  in  multiple  identically-named entries in the environment passed to the shell's children.  Care should be taken in cases where
       this may cause a problem.

       Functions may be recursive.  The FUNCNEST variable may be used to limit the depth of the function call stack and restrict the number of
       function invocations.  By default, no limit is imposed on the number of recursive calls.

ARITHMETIC EVALUATION

       The  shell  allows  arithmetic  expressions  to be evaluated, under certain circumstances (see the let and declare builtin commands and
       Arithmetic Expansion).  Evaluation is done in fixed-width integers with no check for overflow, though division  by  0  is  trapped  and
       flagged  as  an error.  The operators and their precedence, associativity, and values are the same as in the C language.  The following
       list of operators is grouped into levels of equal-precedence operators.  The levels are listed in order of decreasing precedence.

       id++ id--
              variable post-increment and post-decrement
       ++id --id
              variable pre-increment and pre-decrement
       - +    unary minus and plus
       ! ~    logical and bitwise negation
       **     exponentiation
       * / %  multiplication, division, remainder
       + -    addition, subtraction
       << >>  left and right bitwise shifts
       <= >= < >
              comparison
       == !=  equality and inequality
       &      bitwise AND
       ^      bitwise exclusive OR
       |      bitwise OR
       &&     logical AND
       ||     logical OR
       expr?expr:expr
              conditional operator
       = *= /= %= += -= <<= >>= &= ^= |=
              assignment
       expr1 , expr2
              comma

       Shell variables are allowed as operands; parameter expansion is performed before the expression is evaluated.   Within  an  expression,
       shell  variables  may  also be referenced by name without using the parameter expansion syntax.  A shell variable that is null or unset
       evaluates to 0 when referenced by name without using the parameter expansion syntax.  The value  of  a  variable  is  evaluated  as  an
       arithmetic expression when it is referenced, or when a variable which has been given the integer attribute using declare -i is assigned
       a value.  A null value evaluates to 0.  A shell variable need not have its integer attribute turned on to be used in an expression.

       Constants with a leading 0 are interpreted as octal numbers.  A leading 0x or 0X denotes hexadecimal.  Otherwise, numbers take the form
       [base#]n,  where  the  optional  base  is a decimal number between 2 and 64 representing the arithmetic base, and n is a number in that
       base.  If base# is omitted, then base 10 is used.  The digits greater than 9 are represented by the lowercase  letters,  the  uppercase
       letters,  @, and _, in that order.  If base is less than or equal to 36, lowercase and uppercase letters may be used interchangeably to
       represent numbers between 10 and 35.

       Operators are evaluated in order of precedence.  Sub-expressions in parentheses are evaluated first and  may  override  the  precedence
       rules above.

CONDITIONAL EXPRESSIONS

       Conditional  expressions  are  used  by the [[ compound command and the test and [ builtin commands to test file attributes and perform
       string and arithmetic comparisons.  Expressions are formed from the following unary or binary primaries.  If any file argument  to  one
       of  the  primaries is of the form /dev/fd/n, then file descriptor n is checked.  If the file argument to one of the primaries is one of
       /dev/stdin, /dev/stdout, or /dev/stderr, file descriptor 0, 1, or 2, respectively, is checked.

       Unless otherwise specified, primaries that operate on files follow symbolic links and operate on the target of the  link,  rather  than
       the link itself.

       When used with [[, the < and > operators sort lexicographically using the current locale.  The test command sorts using ASCII ordering.

       -a file
              True if file exists.
       -b file
              True if file exists and is a block special file.
       -c file
              True if file exists and is a character special file.
       -d file
              True if file exists and is a directory.
       -e file
              True if file exists.
       -f file
              True if file exists and is a regular file.
       -g file
              True if file exists and is set-group-id.
       -h file
              True if file exists and is a symbolic link.
       -k file
              True if file exists and its ``sticky'' bit is set.
       -p file
              True if file exists and is a named pipe (FIFO).
       -r file
              True if file exists and is readable.
       -s file
              True if file exists and has a size greater than zero.
       -t fd  True if file descriptor fd is open and refers to a terminal.
       -u file
              True if file exists and its set-user-id bit is set.
       -w file
              True if file exists and is writable.
       -x file
              True if file exists and is executable.
       -G file
              True if file exists and is owned by the effective group id.
       -L file
              True if file exists and is a symbolic link.
       -N file
              True if file exists and has been modified since it was last read.
       -O file
              True if file exists and is owned by the effective user id.
       -S file
              True if file exists and is a socket.
       file1 -ef file2
              True if file1 and file2 refer to the same device and inode numbers.
       file1 -nt file2
              True if file1 is newer (according to modification date) than file2, or if file1 exists and file2 does not.
       file1 -ot file2
              True if file1 is older than file2, or if file2 exists and file1 does not.
       -o optname
              True  if the shell option optname is enabled.  See the list of options under the description of the -o option to the set builtin
              below.
       -v varname
              True if the shell variable varname is set (has been assigned a value).
       -z string
              True if the length of string is zero.
       string
       -n string
              True if the length of string is non-zero.

       string1 == string2
       string1 = string2
              True if the strings are equal.  = should be used with the test command for POSIX conformance.

       string1 != string2
              True if the strings are not equal.

       string1 < string2
              True if string1 sorts before string2 lexicographically.

       string1 > string2
              True if string1 sorts after string2 lexicographically.

       arg1 OP arg2
              OP is one of -eq, -ne, -lt, -le, -gt, or -ge.  These arithmetic binary operators return true if arg1 is equal to, not equal  to,
              less  than,  less than or equal to, greater than, or greater than or equal to arg2, respectively.  Arg1 and arg2 may be positive
              or negative integers.

SIMPLE COMMAND EXPANSION

       When a simple command is executed, the shell performs the following expansions, assignments, and redirections, from left to right.

       1.     The words that the parser has marked as variable assignments (those preceding the command name) and redirections are  saved  for
              later processing.

       2.     The  words  that are not variable assignments or redirections are expanded.  If any words remain after expansion, the first word
              is taken to be the name of the command and the remaining words are the arguments.

       3.     Redirections are performed as described above under REDIRECTION.

       4.     The text after the = in  each  variable  assignment  undergoes  tilde  expansion,  parameter  expansion,  command  substitution,
              arithmetic expansion, and quote removal before being assigned to the variable.

       If  no  command name results, the variable assignments affect the current shell environment.  Otherwise, the variables are added to the
       environment of the executed command and do not affect the current shell environment.  If any of the assignments attempts  to  assign  a
       value to a readonly variable, an error occurs, and the command exits with a non-zero status.

       If  no  command  name results, redirections are performed, but do not affect the current shell environment.  A redirection error causes
       the command to exit with a non-zero status.

       If there is a command name left after expansion, execution proceeds as described below.  Otherwise, the command exits.  If one  of  the
       expansions  contained  a  command  substitution,  the  exit  status  of the command is the exit status of the last command substitution
       performed.  If there were no command substitutions, the command exits with a status of zero.

COMMAND EXECUTION

       After a command has been split into words, if it results in a simple command and an optional list of arguments, the  following  actions
       are taken.

       If the command name contains no slashes, the shell attempts to locate it.  If there exists a shell function by that name, that function
       is invoked as described above in FUNCTIONS.  If the name does not match a function, the shell searches for it  in  the  list  of  shell
       builtins.  If a match is found, that builtin is invoked.

       If  the name is neither a shell function nor a builtin, and contains no slashes, bash searches each element of the PATH for a directory
       containing an executable file by that name.  Bash uses a hash table to remember the full pathnames of executable files (see hash  under
       SHELL  BUILTIN  COMMANDS  below).   A  full search of the directories in PATH is performed only if the command is not found in the hash
       table.  If the search is unsuccessful, the shell searches for  a  defined  shell  function  named  command_not_found_handle.   If  that
       function exists, it is invoked with the original command and the original command's arguments as its arguments, and the function's exit
       status becomes the exit status of the shell.  If that function is not defined, the shell prints an error message and  returns  an  exit
       status of 127.

       If  the  search  is successful, or if the command name contains one or more slashes, the shell executes the named program in a separate
       execution environment.  Argument 0 is set to the name given, and the remaining arguments to the command are set to the arguments given,
       if any.

       If  this  execution  fails  because  the file is not in executable format, and the file is not a directory, it is assumed to be a shell
       script, a file containing shell commands.  A subshell is spawned to execute it.  This subshell reinitializes itself, so that the effect
       is  as if a new shell had been invoked to handle the script, with the exception that the locations of commands remembered by the parent
       (see hash below under SHELL BUILTIN COMMANDS) are retained by the child.

       If the program is a file beginning with #!, the remainder of the first line specifies  an  interpreter  for  the  program.   The  shell
       executes  the  specified  interpreter  on operating systems that do not handle this executable format themselves.  The arguments to the
       interpreter consist of a single optional argument following the interpreter name on the first line of the program, followed by the name
       of the program, followed by the command arguments, if any.

COMMAND EXECUTION ENVIRONMENT

       The shell has an execution environment, which consists of the following:

       ·      open files inherited by the shell at invocation, as modified by redirections supplied to the exec builtin

       ·      the current working directory as set by cd, pushd, or popd, or inherited by the shell at invocation

       ·      the file creation mode mask as set by umask or inherited from the shell's parent

       ·      current traps set by trap

       ·      shell parameters that are set by variable assignment or with set or inherited from the shell's parent in the environment

       ·      shell functions defined during execution or inherited from the shell's parent in the environment

       ·      options enabled at invocation (either by default or with command-line arguments) or by set

       ·      options enabled by shopt

       ·      shell aliases defined with alias

       ·      various process IDs, including those of background jobs, the value of $$, and the value of PPID

       When  a simple command other than a builtin or shell function is to be executed, it is invoked in a separate execution environment that
       consists of the following.  Unless otherwise noted, the values are inherited from the shell.

       ·      the shell's open files, plus any modifications and additions specified by redirections to the command

       ·      the current working directory

       ·      the file creation mode mask

       ·      shell variables and functions marked for export, along with variables exported for the command, passed in the environment

       ·      traps caught by the shell are reset to the values inherited from the shell's parent, and traps ignored by the shell are ignored

       A command invoked in this separate environment cannot affect the shell's execution environment.

       Command substitution, commands grouped with parentheses, and asynchronous commands are invoked in a  subshell  environment  that  is  a
       duplicate  of  the  shell  environment, except that traps caught by the shell are reset to the values that the shell inherited from its
       parent at invocation.  Builtin commands that are invoked as part of a pipeline are also executed in a  subshell  environment.   Changes
       made to the subshell environment cannot affect the shell's execution environment.

       Subshells  spawned  to execute command substitutions inherit the value of the -e option from the parent shell.  When not in posix mode,
       bash clears the -e option in such subshells.

       If a command is followed by a & and job control is not active, the default standard input for the command is the empty file  /dev/null.
       Otherwise, the invoked command inherits the file descriptors of the calling shell as modified by redirections.

ENVIRONMENT

       When  a  program  is  invoked  it is given an array of strings called the environment.  This is a list of name-value pairs, of the form
       name=value.

       The shell provides several ways to manipulate the environment.  On invocation, the shell  scans  its  own  environment  and  creates  a
       parameter for each name found, automatically marking it for export to child processes.  Executed commands inherit the environment.  The
       export and declare -x commands allow parameters and functions to be added to and deleted from the  environment.   If  the  value  of  a
       parameter  in the environment is modified, the new value becomes part of the environment, replacing the old.  The environment inherited
       by any executed command consists of the shell's initial environment, whose values may be modified in the shell, less any pairs  removed
       by the unset command, plus any additions via the export and declare -x commands.

       The  environment  for  any  simple  command  or  function  may  be augmented temporarily by prefixing it with parameter assignments, as
       described above in PARAMETERS.  These assignment statements affect only the environment seen by that command.

       If the -k option is set (see the set builtin command below), then all parameter  assignments  are  placed  in  the  environment  for  a
       command, not just those that precede the command name.

       When  bash  invokes  an  external command, the variable _ is set to the full file name of the command and passed to that command in its
       environment.

EXIT STATUS

       The exit status of an executed command is the value returned by the waitpid system call or equivalent  function.   Exit  statuses  fall
       between  0  and  255,  though, as explained below, the shell may use values above 125 specially.  Exit statuses from shell builtins and
       compound commands are also limited to this range. Under certain circumstances, the shell will use special values to  indicate  specific
       failure modes.

       For  the  shell's  purposes, a command which exits with a zero exit status has succeeded.  An exit status of zero indicates success.  A
       non-zero exit status indicates failure.  When a command terminates on a fatal signal N, bash uses  the  value  of  128+N  as  the  exit
       status.

       If  a  command  is  not  found,  the  child  process  created  to execute it returns a status of 127.  If a command is found but is not
       executable, the return status is 126.

       If a command fails because of an error during expansion or redirection, the exit status is greater than zero.

       Shell builtin commands return a status of 0 (true) if successful, and non-zero (false) if an error  occurs  while  they  execute.   All
       builtins return an exit status of 2 to indicate incorrect usage.

       Bash  itself returns the exit status of the last command executed, unless a syntax error occurs, in which case it exits with a non-zero
       value.  See also the exit builtin command below.

SIGNALS

       When bash is interactive, in the absence of any traps, it ignores SIGTERM (so that kill 0 does not  kill  an  interactive  shell),  and
       SIGINT  is  caught  and handled (so that the wait builtin is interruptible).  In all cases, bash ignores SIGQUIT.  If job control is in
       effect, bash ignores SIGTTIN, SIGTTOU, and SIGTSTP.

       Non-builtin commands run by bash have signal handlers set to the values inherited by the shell from its parent.  When  job  control  is
       not  in  effect,  asynchronous commands ignore SIGINT and SIGQUIT in addition to these inherited handlers.  Commands run as a result of
       command substitution ignore the keyboard-generated job control signals SIGTTIN, SIGTTOU, and SIGTSTP.

       The shell exits by default upon receipt of a SIGHUP.  Before exiting, an interactive shell resends the SIGHUP to all jobs,  running  or
       stopped.   Stopped  jobs  are  sent  SIGCONT to ensure that they receive the SIGHUP.  To prevent the shell from sending the signal to a
       particular job, it should be removed from the jobs table with the disown builtin (see SHELL BUILTIN COMMANDS below) or  marked  to  not
       receive SIGHUP using disown -h.

       If the huponexit shell option has been set with shopt, bash sends a SIGHUP to all jobs when an interactive login shell exits.

       If  bash  is waiting for a command to complete and receives a signal for which a trap has been set, the trap will not be executed until
       the command completes.  When bash is waiting for an asynchronous command via the wait builtin, the reception of a signal  for  which  a
       trap  has  been set will cause the wait builtin to return immediately with an exit status greater than 128, immediately after which the
       trap is executed.

JOB CONTROL

       Job control refers to the ability to selectively stop (suspend) the execution of processes and continue (resume) their execution  at  a
       later  point.   A  user  typically employs this facility via an interactive interface supplied jointly by the operating system kernel's
       terminal driver and bash.

       The shell associates a job with each pipeline.  It keeps a table of currently executing  jobs,  which  may  be  listed  with  the  jobs
       command.  When bash starts a job asynchronously (in the background), it prints a line that looks like:

              [1] 25647

       indicating that this job is job number 1 and that the process ID of the last process in the pipeline associated with this job is 25647.
       All of the processes in a single pipeline are members of the same job.  Bash uses the job abstraction as the basis for job control.

       To facilitate the implementation of the user interface to job control, the operating system maintains the notion of a current  terminal
       process  group  ID.  Members of this process group (processes whose process group ID is equal to the current terminal process group ID)
       receive keyboard-generated signals such as SIGINT.  These processes are said to be in the foreground.  Background processes  are  those
       whose process group ID differs from the terminal's; such processes are immune to keyboard-generated signals.  Only foreground processes
       are allowed to read from or, if the user so specifies with stty tostop, write to the terminal.  Background processes which  attempt  to
       read  from  (write  to when stty tostop is in effect) the terminal are sent a SIGTTIN (SIGTTOU) signal by the kernel's terminal driver,
       which, unless caught, suspends the process.

       If the operating system on which bash is running supports job control,  bash  contains  facilities  to  use  it.   Typing  the  suspend
       character  (typically  ^Z, Control-Z) while a process is running causes that process to be stopped and returns control to bash.  Typing
       the delayed suspend character (typically ^Y, Control-Y) causes the process to be stopped when  it  attempts  to  read  input  from  the
       terminal,  and control to be returned to bash.  The user may then manipulate the state of this job, using the bg command to continue it
       in the background, the fg command to continue it in the foreground, or the kill command to kill it.  A ^Z takes effect immediately, and
       has the additional side effect of causing pending output and typeahead to be discarded.

       There are a number of ways to refer to a job in the shell.  The character % introduces a job specification (jobspec).  Job number n may
       be referred to as %n.  A job may also be referred to using a prefix of the name used to start it, or using a substring that appears  in
       its  command  line.  For example, %ce refers to a stopped ce job.  If a prefix matches more than one job, bash reports an error.  Using
       %?ce, on the other hand, refers to any job containing the string ce in its command line.  If the substring matches more than  one  job,
       bash  reports  an  error.  The symbols %% and %+ refer to the shell's notion of the current job, which is the last job stopped while it
       was in the foreground or started in the background.  The previous job may be referenced using %-.  If there is only a  single  job,  %+
       and  %- can both be used to refer to that job.  In output pertaining to jobs (e.g., the output of the jobs command), the current job is
       always flagged with a +, and the previous job with a -.  A single % (with no accompanying job specification) also refers to the current
       job.

       Simply naming a job can be used to bring it into the foreground: %1 is a synonym for ``fg %1'', bringing job 1 from the background into
       the foreground.  Similarly, ``%1 &'' resumes job 1 in the background, equivalent to ``bg %1''.

       The shell learns immediately whenever a job changes state.  Normally, bash waits until it is about to print a prompt  before  reporting
       changes  in  a  job's  status  so  as  to not interrupt any other output.  If the -b option to the set builtin command is enabled, bash
       reports such changes immediately.  Any trap on SIGCHLD is executed for each child that exits.

       If an attempt to exit bash is made while jobs are stopped (or, if the checkjobs shell option has been enabled using the shopt  builtin,
       running),  the  shell  prints  a warning message, and, if the checkjobs option is enabled, lists the jobs and their statuses.  The jobs
       command may then be used to inspect their status.  If a second attempt to exit is made without an intervening command, the  shell  does
       not print another warning, and any stopped jobs are terminated.

PROMPTING

       When  executing  interactively,  bash  displays the primary prompt PS1 when it is ready to read a command, and the secondary prompt PS2
       when it needs more input to complete a command.  Bash allows these prompt strings to be customized by inserting a number of  backslash-
       escaped special characters that are decoded as follows:
              \a     an ASCII bell character (07)
              \d     the date in "Weekday Month Date" format (e.g., "Tue May 26")
              \D{format}
                     the  format  is  passed  to  strftime(3)  and the result is inserted into the prompt string; an empty format results in a
                     locale-specific time representation.  The braces are required
              \e     an ASCII escape character (033)
              \h     the hostname up to the first `.'
              \H     the hostname
              \j     the number of jobs currently managed by the shell
              \l     the basename of the shell's terminal device name
              \n     newline
              \r     carriage return
              \s     the name of the shell, the basename of $0 (the portion following the final slash)
              \t     the current time in 24-hour HH:MM:SS format
              \T     the current time in 12-hour HH:MM:SS format
              \@     the current time in 12-hour am/pm format
              \A     the current time in 24-hour HH:MM format
              \u     the username of the current user
              \v     the version of bash (e.g., 2.00)
              \V     the release of bash, version + patch level (e.g., 2.00.0)
              \w     the current working directory, with $HOME abbreviated with a tilde (uses the value of the PROMPT_DIRTRIM variable)
              \W     the basename of the current working directory, with $HOME abbreviated with a tilde
              \!     the history number of this command
              \#     the command number of this command
              \$     if the effective UID is 0, a #, otherwise a $
              \nnn   the character corresponding to the octal number nnn
              \\     a backslash
              \[     begin a sequence of non-printing characters, which could be used to embed a terminal control sequence into the prompt
              \]     end a sequence of non-printing characters

       The command number and the history number are usually different: the history number of a command is its position in the  history  list,
       which may include commands restored from the history file (see HISTORY below), while the command number is the position in the sequence
       of commands executed during the current shell session.  After the string is decoded, it is expanded via  parameter  expansion,  command
       substitution,  arithmetic expansion, and quote removal, subject to the value of the promptvars shell option (see the description of the
       shopt command under SHELL BUILTIN COMMANDS below).

READLINE

       This is the library that handles reading input when using an interactive shell,  unless  the  --noediting  option  is  given  at  shell
       invocation.  Line editing is also used when using the -e option to the read builtin.  By default, the line editing commands are similar
       to those of Emacs.  A vi-style line editing interface is also available.  Line editing can be enabled at any time using the -o emacs or
       -o  vi  options to the set builtin (see SHELL BUILTIN COMMANDS below).  To turn off line editing after the shell is running, use the +o
       emacs or +o vi options to the set builtin.

   Readline Notation
       In this section, the Emacs-style notation is used to denote keystrokes.  Control keys are denoted by C-key, e.g., C-n means  Control-N.
       Similarly,  meta  keys  are  denoted by M-key, so M-x means Meta-X.  (On keyboards without a meta key, M-x means ESC x, i.e., press the
       Escape key then the x key.  This makes ESC the meta prefix.  The combination M-C-x means ESC-Control-x, or press the  Escape  key  then
       hold the Control key while pressing the x key.)

       Readline  commands  may  be  given  numeric arguments, which normally act as a repeat count.  Sometimes, however, it is the sign of the
       argument that is significant.  Passing a negative argument to a command that acts in the forward  direction  (e.g.,  kill-line)  causes
       that command to act in a backward direction.  Commands whose behavior with arguments deviates from this are noted below.

       When  a  command  is  described as killing text, the text deleted is saved for possible future retrieval (yanking).  The killed text is
       saved in a kill ring.  Consecutive kills cause the text to be accumulated into one unit, which can be yanked  all  at  once.   Commands
       which do not kill text separate the chunks of text on the kill ring.

   Readline Initialization
       Readline is customized by putting commands in an initialization file (the inputrc file).  The name of this file is taken from the value
       of the INPUTRC variable.  If that variable is unset, the default is ~/.inputrc.  When a program which uses the readline library  starts
       up,  the initialization file is read, and the key bindings and variables are set.  There are only a few basic constructs allowed in the
       readline initialization file.  Blank lines are ignored.  Lines beginning with a # are comments.  Lines  beginning  with  a  $  indicate
       conditional constructs.  Other lines denote key bindings and variable settings.

       The  default  key-bindings  may  be  changed with an inputrc file.  Other programs that use this library may add their own commands and
       bindings.

       For example, placing

              M-Control-u: universal-argument
       or
              C-Meta-u: universal-argument
       into the inputrc would make M-C-u execute the readline command universal-argument.

       The following symbolic character names are recognized: RUBOUT, DEL, ESC, LFD, NEWLINE, RET, RETURN, SPC, SPACE, and TAB.

       In addition to command names, readline allows keys to be bound to a string that is inserted when the key is pressed (a macro).

   Readline Key Bindings
       The syntax for controlling key bindings in the inputrc file is simple.  All that is required is the name of the command or the text  of
       a  macro and a key sequence to which it should be bound. The name may be specified in one of two ways: as a symbolic key name, possibly
       with Meta- or Control- prefixes, or as a key sequence.

       When using the form keyname:function-name or macro, keyname is the name of a key spelled out in English.  For example:

              Control-u: universal-argument
              Meta-Rubout: backward-kill-word
              Control-o: "> output"

       In the above example, C-u is bound to the function universal-argument, M-DEL is bound to the function backward-kill-word,  and  C-o  is
       bound to run the macro expressed on the right hand side (that is, to insert the text ``> output'' into the line).

       In  the second form, "keyseq":function-name or macro, keyseq differs from keyname above in that strings denoting an entire key sequence
       may be specified by placing the sequence within double quotes.  Some GNU Emacs style key escapes can  be  used,  as  in  the  following
       example, but the symbolic character names are not recognized.

              "\C-u": universal-argument
              "\C-x\C-r": re-read-init-file
              "\e[11~": "Function Key 1"

       In  this example, C-u is again bound to the function universal-argument.  C-x C-r is bound to the function re-read-init-file, and ESC [
       1 1 ~ is bound to insert the text ``Function Key 1''.

       The full set of GNU Emacs style escape sequences is
              \C-    control prefix
              \M-    meta prefix
              \e     an escape character
              \\     backslash
              \"     literal "
              \'     literal '

       In addition to the GNU Emacs style escape sequences, a second set of backslash escapes is available:
              \a     alert (bell)
              \b     backspace
              \d     delete
              \f     form feed
              \n     newline
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \nnn   the eight-bit character whose value is the octal value nnn (one to three digits)
              \xHH   the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)

       When entering the text of a macro, single or double quotes must be used to indicate a macro definition.  Unquoted text is assumed to be
       a  function  name.  In the macro body, the backslash escapes described above are expanded.  Backslash will quote any other character in
       the macro text, including " and '.

       Bash allows the current readline key bindings to be displayed or modified with the bind builtin  command.   The  editing  mode  may  be
       switched during interactive use by using the -o option to the set builtin command (see SHELL BUILTIN COMMANDS below).

   Readline Variables
       Readline  has variables that can be used to further customize its behavior.  A variable may be set in the inputrc file with a statement
       of the form

              set variable-name value

       Except where noted, readline variables can take the values On or Off  (without  regard  to  case).   Unrecognized  variable  names  are
       ignored.  When a variable value is read, empty or null values, "on" (case-insensitive), and "1" are equivalent to On.  All other values
       are equivalent to Off.  The variables and their default values are:

       bell-style (audible)
              Controls what happens when readline wants to ring the terminal bell.  If set to none, readline never rings the bell.  If set  to
              visible, readline uses a visible bell if one is available.  If set to audible, readline attempts to ring the terminal's bell.
       bind-tty-special-chars (On)
              If  set  to  On,  readline  attempts  to  bind the control characters treated specially by the kernel's terminal driver to their
              readline equivalents.
       comment-begin (``#'')
              The string that is inserted when the readline insert-comment command is executed.  This command is bound to M-#  in  emacs  mode
              and to # in vi command mode.
       completion-ignore-case (Off)
              If set to On, readline performs filename matching and completion in a case-insensitive fashion.
       completion-prefix-display-length (0)
              The  length  in  characters of the common prefix of a list of possible completions that is displayed without modification.  When
              set to a value greater than zero, common prefixes longer than this value are replaced with an ellipsis when displaying  possible
              completions.
       completion-query-items (100)
              This  determines when the user is queried about viewing the number of possible completions generated by the possible-completions
              command.  It may be set to any integer value greater than or equal to zero.  If the number of possible  completions  is  greater
              than  or equal to the value of this variable, the user is asked whether or not he wishes to view them; otherwise they are simply
              listed on the terminal.
       convert-meta (On)
              If set to On, readline will convert characters with the eighth bit set to an ASCII key sequence by stripping the eighth bit  and
              prefixing an escape character (in effect, using escape as the meta prefix).
       disable-completion (Off)
              If  set  to On, readline will inhibit word completion.  Completion characters will be inserted into the line as if they had been
              mapped to self-insert.
       editing-mode (emacs)
              Controls whether readline begins with a set of key bindings similar to Emacs or vi.  editing-mode can be set to either emacs  or
              vi.
       echo-control-characters (On)
              When  set  to  On,  on  operating  systems  that indicate they support it, readline echoes a character corresponding to a signal
              generated from the keyboard.
       enable-keypad (Off)
              When set to On, readline will try to enable the application keypad when it is called.  Some systems  need  this  to  enable  the
              arrow keys.
       enable-meta-key (On)
              When  set  to  On,  readline will try to enable any meta modifier key the terminal claims to support when it is called.  On many
              terminals, the meta key is used to send eight-bit characters.
       expand-tilde (Off)
              If set to On, tilde expansion is performed when readline attempts word completion.
       history-preserve-point (Off)
              If set to On, the history code attempts to place point at the same location on each history line retrieved with previous-history
              or next-history.
       history-size (0)
              Set  the maximum number of history entries saved in the history list.  If set to zero, the number of entries in the history list
              is not limited.
       horizontal-scroll-mode (Off)
              When set to On, makes readline use a single line for display, scrolling the input horizontally on a single screen line  when  it
              becomes longer than the screen width rather than wrapping to a new line.
       input-meta (Off)
              If  set  to  On,  readline  will  enable eight-bit input (that is, it will not strip the high bit from the characters it reads),
              regardless of what the terminal claims it can support.  The name meta-flag is a synonym for this variable.
       isearch-terminators (``C-[C-J'')
              The string of characters that should terminate an incremental search without subsequently executing the character as a  command.
              If this variable has not been given a value, the characters ESC and C-J will terminate an incremental search.
       keymap (emacs)
              Set  the  current  readline  keymap.   The  set  of  valid  keymap  names  is emacs, emacs-standard, emacs-meta, emacs-ctlx, vi,
              vi-command, and vi-insert.  vi is equivalent to vi-command; emacs is equivalent to emacs-standard.  The default value is  emacs;
              the value of editing-mode also affects the default keymap.
       mark-directories (On)
              If set to On, completed directory names have a slash appended.
       mark-modified-lines (Off)
              If set to On, history lines that have been modified are displayed with a preceding asterisk (*).
       mark-symlinked-directories (Off)
              If  set  to  On,  completed  names  which  are  symbolic  links  to  directories  have a slash appended (subject to the value of
              mark-directories).
       match-hidden-files (On)
              This variable, when set to On, causes readline to match files whose names begin  with  a  `.'  (hidden  files)  when  performing
              filename completion.  If set to Off, the leading `.' must be supplied by the user in the filename to be completed.
       menu-complete-display-prefix (Off)
              If set to On, menu completion displays the common prefix of the list of possible completions (which may be empty) before cycling
              through the list.
       output-meta (Off)
              If set to On, readline will display characters with the eighth bit set directly rather than as a meta-prefixed escape sequence.
       page-completions (On)
              If set to On, readline uses an internal more-like pager to display a screenful of possible completions at a time.
       print-completions-horizontally (Off)
              If set to On, readline will display completions with matches sorted horizontally in alphabetical order,  rather  than  down  the
              screen.
       revert-all-at-newline (Off)
              If  set  to  On,  readline  will  undo  all changes to history lines before returning when accept-line is executed.  By default,
              history lines may be modified and retain individual undo lists across calls to readline.
       show-all-if-ambiguous (Off)
              This alters the default behavior of the completion functions.  If set to On, words which have more than one possible  completion
              cause the matches to be listed immediately instead of ringing the bell.
       show-all-if-unmodified (Off)
              This alters the default behavior of the completion functions in a fashion similar to show-all-if-ambiguous.  If set to On, words
              which have more than one possible completion without any possible partial completion (the possible  completions  don't  share  a
              common prefix) cause the matches to be listed immediately instead of ringing the bell.
       skip-completed-text (Off)
              If  set  to  On, this alters the default completion behavior when inserting a single match into the line.  It's only active when
              performing completion in the middle of a word.  If enabled, readline does not insert characters from the completion  that  match
              characters after point in the word being completed, so portions of the word following the cursor are not duplicated.
       visible-stats (Off)
              If  set  to  On,  a  character  denoting  a file's type as reported by stat(2) is appended to the filename when listing possible
              completions.

   Readline Conditional Constructs
       Readline implements a facility similar in spirit to the conditional compilation  features  of  the  C  preprocessor  which  allows  key
       bindings and variable settings to be performed as the result of tests.  There are four parser directives used.

       $if    The  $if  construct  allows  bindings  to  be  made based on the editing mode, the terminal being used, or the application using
              readline.  The text of the test extends to the end of the line; no characters are required to isolate it.

              mode   The mode= form of the $if directive is used to test whether readline is in emacs  or  vi  mode.   This  may  be  used  in
                     conjunction  with the set keymap command, for instance, to set bindings in the emacs-standard and emacs-ctlx keymaps only
                     if readline is starting out in emacs mode.

              term   The term= form may be used to include terminal-specific key bindings, perhaps to bind the key  sequences  output  by  the
                     terminal's  function  keys.  The word on the right side of the = is tested against the both full name of the terminal and
                     the portion of the terminal name before the first -.  This allows sun to match both sun and sun-cmd, for instance.

              application
                     The application construct is used to include application-specific settings.  Each program using the readline library sets
                     the  application  name,  and  an  initialization  file  can  test for a particular value.  This could be used to bind key
                     sequences to functions useful for a specific program.  For instance, the following  command  adds  a  key  sequence  that
                     quotes the current or previous word in bash:

                     $if Bash
                     # Quote the current or previous word
                     "\C-xq": "\eb\"\ef\""
                     $endif

       $endif This command, as seen in the previous example, terminates an $if command.

       $else  Commands in this branch of the $if directive are executed if the test fails.

       $include
              This  directive  takes  a  single  filename  as  an  argument  and reads commands and bindings from that file.  For example, the
              following directive would read /etc/inputrc:

              $include  /etc/inputrc

   Searching
       Readline provides commands for searching through the command history (see HISTORY below)  for  lines  containing  a  specified  string.
       There are two search modes: incremental and non-incremental.

       Incremental  searches  begin  before  the user has finished typing the search string.  As each character of the search string is typed,
       readline displays the next entry from the history matching the string typed so far.   An  incremental  search  requires  only  as  many
       characters  as  needed  to find the desired history entry.  The characters present in the value of the isearch-terminators variable are
       used to terminate an incremental search.  If that variable has not been assigned a value  the  Escape  and  Control-J  characters  will
       terminate  an  incremental  search.   Control-G  will  abort  an  incremental search and restore the original line.  When the search is
       terminated, the history entry containing the search string becomes the current line.

       To find other matching entries in the history list, type Control-S or Control-R as appropriate.  This will search backward  or  forward
       in  the  history  for  the next entry matching the search string typed so far.  Any other key sequence bound to a readline command will
       terminate the search and execute that command.  For instance, a newline  will  terminate  the  search  and  accept  the  line,  thereby
       executing the command from the history list.

       Readline  remembers  the last incremental search string.  If two Control-Rs are typed without any intervening characters defining a new
       search string, any remembered search string is used.

       Non-incremental searches read the entire search string before starting to search for matching history lines.  The search string may  be
       typed by the user or be part of the contents of the current line.

   Readline Command Names
       The  following  is a list of the names of the commands and the default key sequences to which they are bound.  Command names without an
       accompanying key sequence are unbound by default.  In the following descriptions, point refers to the current cursor position, and mark
       refers to a cursor position saved by the set-mark command.  The text between the point and mark is referred to as the region.

   Commands for Moving
       beginning-of-line (C-a)
              Move to the start of the current line.
       end-of-line (C-e)
              Move to the end of the line.
       forward-char (C-f)
              Move forward a character.
       backward-char (C-b)
              Move back a character.
       forward-word (M-f)
              Move forward to the end of the next word.  Words are composed of alphanumeric characters (letters and digits).
       backward-word (M-b)
              Move back to the start of the current or previous word.  Words are composed of alphanumeric characters (letters and digits).
       shell-forward-word
              Move forward to the end of the next word.  Words are delimited by non-quoted shell metacharacters.
       shell-backward-word
              Move back to the start of the current or previous word.  Words are delimited by non-quoted shell metacharacters.
       clear-screen (C-l)
              Clear the screen leaving the current line at the top of the screen.  With an argument, refresh the current line without clearing
              the screen.
       redraw-current-line
              Refresh the current line.

   Commands for Manipulating the History
       accept-line (Newline, Return)
              Accept the line regardless of where the cursor is.  If this line is non-empty, add it to the history list according to the state
              of the HISTCONTROL variable.  If the line is a modified history line, then restore the history line to its original state.
       previous-history (C-p)
              Fetch the previous command from the history list, moving back in the list.
       next-history (C-n)
              Fetch the next command from the history list, moving forward in the list.
       beginning-of-history (M-<)
              Move to the first line in the history.
       end-of-history (M->)
              Move to the end of the input history, i.e., the line currently being entered.
       reverse-search-history (C-r)
              Search backward starting at the current line and moving `up' through the history as necessary.  This is an incremental search.
       forward-search-history (C-s)
              Search forward starting at the current line and moving `down' through the history as necessary.  This is an incremental search.
       non-incremental-reverse-search-history (M-p)
              Search  backward  through  the  history starting at the current line using a non-incremental search for a string supplied by the
              user.
       non-incremental-forward-search-history (M-n)
              Search forward through the history using a non-incremental search for a string supplied by the user.
       history-search-forward
              Search forward through the history for the string of characters between the start of the current line and the point.  This is  a
              non-incremental search.
       history-search-backward
              Search backward through the history for the string of characters between the start of the current line and the point.  This is a
              non-incremental search.
       yank-nth-arg (M-C-y)
              Insert the first argument to the previous command (usually the second word on the previous line) at point.  With an argument  n,
              insert  the  nth  word  from  the  previous  command (the words in the previous command begin with word 0).  A negative argument
              inserts the nth word from the end of the previous command.  Once the argument n is computed, the argument is extracted as if the
              "!n" history expansion had been specified.
       yank-last-arg (M-., M-_)
              Insert the last argument to the previous command (the last word of the previous history entry).  With a numeric argument, behave
              exactly like yank-nth-arg.  Successive calls to yank-last-arg move back through the history list, inserting the  last  word  (or
              the  word  specified by the argument to the first call) of each line in turn.  Any numeric argument supplied to these successive
              calls determines the direction to move through the history.  A negative argument switches  the  direction  through  the  history
              (back or forward).  The history expansion facilities are used to extract the last argument, as if the "!$" history expansion had
              been specified.
       shell-expand-line (M-C-e)
              Expand the line as the shell does.  This performs alias and history expansion as well as all of the shell word expansions.   See
              HISTORY EXPANSION below for a description of history expansion.
       history-expand-line (M-^)
              Perform history expansion on the current line.  See HISTORY EXPANSION below for a description of history expansion.
       magic-space
              Perform  history  expansion  on  the  current line and insert a space.  See HISTORY EXPANSION below for a description of history
              expansion.
       alias-expand-line
              Perform alias expansion on the current line.  See ALIASES above for a description of alias expansion.
       history-and-alias-expand-line
              Perform history and alias expansion on the current line.
       insert-last-argument (M-., M-_)
              A synonym for yank-last-arg.
       operate-and-get-next (C-o)
              Accept the current line for execution and fetch the next line relative to the current line from the history  for  editing.   Any
              argument is ignored.
       edit-and-execute-command (C-xC-e)
              Invoke  an  editor  on  the  current  command  line, and execute the result as shell commands.  Bash attempts to invoke $VISUAL,
              $EDITOR, and emacs as the editor, in that order.

   Commands for Changing Text
       delete-char (C-d)
              Delete the character at point.  If point is at the beginning of the line, there are no characters in  the  line,  and  the  last
              character typed was not bound to delete-char, then return EOF.
       backward-delete-char (Rubout)
              Delete the character behind the cursor.  When given a numeric argument, save the deleted text on the kill ring.
       forward-backward-delete-char
              Delete  the  character  under  the  cursor,  unless the cursor is at the end of the line, in which case the character behind the
              cursor is deleted.
       quoted-insert (C-q, C-v)
              Add the next character typed to the line verbatim.  This is how to insert characters like C-q, for example.
       tab-insert (C-v TAB)
              Insert a tab character.
       self-insert (a, b, A, 1, !, ...)
              Insert the character typed.
       transpose-chars (C-t)
              Drag the character before point forward over the character at point, moving point forward as well.  If point is at  the  end  of
              the line, then this transposes the two characters before point.  Negative arguments have no effect.
       transpose-words (M-t)
              Drag  the word before point past the word after point, moving point over that word as well.  If point is at the end of the line,
              this transposes the last two words on the line.
       upcase-word (M-u)
              Uppercase the current (or following) word.  With a negative argument, uppercase the previous word, but do not move point.
       downcase-word (M-l)
              Lowercase the current (or following) word.  With a negative argument, lowercase the previous word, but do not move point.
       capitalize-word (M-c)
              Capitalize the current (or following) word.  With a negative argument, capitalize the previous word, but do not move point.
       overwrite-mode
              Toggle overwrite mode.  With an explicit positive numeric argument, switches to overwrite mode.  With an  explicit  non-positive
              numeric argument, switches to insert mode.  This command affects only emacs mode; vi mode does overwrite differently.  Each call
              to readline() starts in insert mode.  In overwrite mode, characters bound to self-insert replace the text at point  rather  than
              pushing  the  text  to the right.  Characters bound to backward-delete-char replace the character before point with a space.  By
              default, this command is unbound.

   Killing and Yanking
       kill-line (C-k)
              Kill the text from point to the end of the line.
       backward-kill-line (C-x Rubout)
              Kill backward to the beginning of the line.
       unix-line-discard (C-u)
              Kill backward from point to the beginning of the line.  The killed text is saved on the kill-ring.
       kill-whole-line
              Kill all characters on the current line, no matter where point is.
       kill-word (M-d)
              Kill from point to the end of the current word, or if between words, to the end of the next word.  Word boundaries are the  same
              as those used by forward-word.
       backward-kill-word (M-Rubout)
              Kill the word behind point.  Word boundaries are the same as those used by backward-word.
       shell-kill-word (M-d)
              Kill  from point to the end of the current word, or if between words, to the end of the next word.  Word boundaries are the same
              as those used by shell-forward-word.
       shell-backward-kill-word (M-Rubout)
              Kill the word behind point.  Word boundaries are the same as those used by shell-backward-word.
       unix-word-rubout (C-w)
              Kill the word behind point, using white space as a word boundary.  The killed text is saved on the kill-ring.
       unix-filename-rubout
              Kill the word behind point, using white space and the slash character as the word boundaries.  The killed text is saved  on  the
              kill-ring.
       delete-horizontal-space (M-\)
              Delete all spaces and tabs around point.
       kill-region
              Kill the text in the current region.
       copy-region-as-kill
              Copy the text in the region to the kill buffer.
       copy-backward-word
              Copy the word before point to the kill buffer.  The word boundaries are the same as backward-word.
       copy-forward-word
              Copy the word following point to the kill buffer.  The word boundaries are the same as forward-word.
       yank (C-y)
              Yank the top of the kill ring into the buffer at point.
       yank-pop (M-y)
              Rotate the kill ring, and yank the new top.  Only works following yank or yank-pop.

   Numeric Arguments
       digit-argument (M-0, M-1, ..., M--)
              Add this digit to the argument already accumulating, or start a new argument.  M-- starts a negative argument.
       universal-argument
              This  is another way to specify an argument.  If this command is followed by one or more digits, optionally with a leading minus
              sign, those digits define the argument.  If the command is followed by  digits,  executing  universal-argument  again  ends  the
              numeric  argument,  but is otherwise ignored.  As a special case, if this command is immediately followed by a character that is
              neither a digit or minus sign, the argument count for the next command is multiplied by four.  The argument count  is  initially
              one,  so  executing  this function the first time makes the argument count four, a second time makes the argument count sixteen,
              and so on.

   Completing
       complete (TAB)
              Attempt to perform completion on the text before point.  Bash attempts completion treating the text as a variable (if  the  text
              begins  with  $),  username (if the text begins with ~), hostname (if the text begins with @), or command (including aliases and
              functions) in turn.  If none of these produces a match, filename completion is attempted.
       possible-completions (M-?)
              List the possible completions of the text before point.
       insert-completions (M-*)
              Insert all completions of the text before point that would have been generated by possible-completions.
       menu-complete
              Similar to complete, but replaces the word to be completed with a single match from the list of possible completions.   Repeated
              execution of menu-complete steps through the list of possible completions, inserting each match in turn.  At the end of the list
              of completions, the bell is rung (subject to the setting of bell-style) and the original text is restored.   An  argument  of  n
              moves  n  positions  forward  in  the  list of matches; a negative argument may be used to move backward through the list.  This
              command is intended to be bound to TAB, but is unbound by default.
       menu-complete-backward
              Identical to menu-complete, but moves backward through the list of possible completions, as if menu-complete had  been  given  a
              negative argument.  This command is unbound by default.
       delete-char-or-list
              Deletes  the  character  under  the  cursor if not at the beginning or end of the line (like delete-char).  If at the end of the
              line, behaves identically to possible-completions.  This command is unbound by default.
       complete-filename (M-/)
              Attempt filename completion on the text before point.
       possible-filename-completions (C-x /)
              List the possible completions of the text before point, treating it as a filename.
       complete-username (M-~)
              Attempt completion on the text before point, treating it as a username.
       possible-username-completions (C-x ~)
              List the possible completions of the text before point, treating it as a username.
       complete-variable (M-$)
              Attempt completion on the text before point, treating it as a shell variable.
       possible-variable-completions (C-x $)
              List the possible completions of the text before point, treating it as a shell variable.
       complete-hostname (M-@)
              Attempt completion on the text before point, treating it as a hostname.
       possible-hostname-completions (C-x @)
              List the possible completions of the text before point, treating it as a hostname.
       complete-command (M-!)
              Attempt completion on the text before point, treating it as a command name.  Command  completion  attempts  to  match  the  text
              against aliases, reserved words, shell functions, shell builtins, and finally executable filenames, in that order.
       possible-command-completions (C-x !)
              List the possible completions of the text before point, treating it as a command name.
       dynamic-complete-history (M-TAB)
              Attempt  completion  on  the  text  before point, comparing the text against lines from the history list for possible completion
              matches.
       dabbrev-expand
              Attempt menu completion on the text before point, comparing the text against lines from the history list for possible completion
              matches.
       complete-into-braces (M-{)
              Perform  filename  completion and insert the list of possible completions enclosed within braces so the list is available to the
              shell (see Brace Expansion above).

   Keyboard Macros
       start-kbd-macro (C-x ()
              Begin saving the characters typed into the current keyboard macro.
       end-kbd-macro (C-x ))
              Stop saving the characters typed into the current keyboard macro and store the definition.
       call-last-kbd-macro (C-x e)
              Re-execute the last keyboard macro defined, by making the characters in the macro appear as if typed at the keyboard.

   Miscellaneous
       re-read-init-file (C-x C-r)
              Read in the contents of the inputrc file, and incorporate any bindings or variable assignments found there.
       abort (C-g)
              Abort the current editing command and ring the terminal's bell (subject to the setting of bell-style).
       do-uppercase-version (M-a, M-b, M-x, ...)
              If the metafied character x is lowercase, run the command that is bound to the corresponding uppercase character.
       prefix-meta (ESC)
              Metafy the next character typed.  ESC f is equivalent to Meta-f.
       undo (C-_, C-x C-u)
              Incremental undo, separately remembered for each line.
       revert-line (M-r)
              Undo all changes made to this line.  This is like executing the undo command enough times to return  the  line  to  its  initial
              state.
       tilde-expand (M-&)
              Perform tilde expansion on the current word.
       set-mark (C-@, M-<space>)
              Set the mark to the point.  If a numeric argument is supplied, the mark is set to that position.
       exchange-point-and-mark (C-x C-x)
              Swap the point with the mark.  The current cursor position is set to the saved position, and the old cursor position is saved as
              the mark.
       character-search (C-])
              A character is read and point is moved to the next occurrence of  that  character.   A  negative  count  searches  for  previous
              occurrences.
       character-search-backward (M-C-])
              A  character  is read and point is moved to the previous occurrence of that character.  A negative count searches for subsequent
              occurrences.
       skip-csi-sequence
              Read enough characters to consume a multi-key sequence such as those defined for keys like Home and End.  Such  sequences  begin
              with  a  Control Sequence Indicator (CSI), usually ESC-[.  If this sequence is bound to "\[", keys producing such sequences will
              have no effect unless explicitly bound to a readline command, instead of inserting stray characters  into  the  editing  buffer.
              This is unbound by default, but usually bound to ESC-[.
       insert-comment (M-#)
              Without  a  numeric argument, the value of the readline comment-begin variable is inserted at the beginning of the current line.
              If a numeric argument is supplied, this command acts as a toggle:  if the characters at the beginning of the line do  not  match
              the  value  of comment-begin, the value is inserted, otherwise the characters in comment-begin are deleted from the beginning of
              the line.  In either case, the line is accepted as if a newline had been typed.  The default value of comment-begin causes  this
              command  to  make  the current line a shell comment.  If a numeric argument causes the comment character to be removed, the line
              will be executed by the shell.
       glob-complete-word (M-g)
              The word before point is treated as a pattern for pathname expansion, with an asterisk implicitly  appended.   This  pattern  is
              used to generate a list of matching file names for possible completions.
       glob-expand-word (C-x *)
              The word before point is treated as a pattern for pathname expansion, and the list of matching file names is inserted, replacing
              the word.  If a numeric argument is supplied, an asterisk is appended before pathname expansion.
       glob-list-expansions (C-x g)
              The list of expansions that would have been generated by glob-expand-word is displayed, and the line is redrawn.  If  a  numeric
              argument is supplied, an asterisk is appended before pathname expansion.
       dump-functions
              Print  all of the functions and their key bindings to the readline output stream.  If a numeric argument is supplied, the output
              is formatted in such a way that it can be made part of an inputrc file.
       dump-variables
              Print all of the settable readline variables and their values to the readline output stream.  If a numeric argument is supplied,
              the output is formatted in such a way that it can be made part of an inputrc file.
       dump-macros
              Print  all  of  the  readline key sequences bound to macros and the strings they output.  If a numeric argument is supplied, the
              output is formatted in such a way that it can be made part of an inputrc file.
       display-shell-version (C-x C-v)
              Display version information about the current instance of bash.

   Programmable Completion
       When word completion is attempted for an argument to a command for which a completion specification (a compspec) has been defined using
       the complete builtin (see SHELL BUILTIN COMMANDS below), the programmable completion facilities are invoked.

       First,  the  command  name  is  identified.  If the command word is the empty string (completion attempted at the beginning of an empty
       line), any compspec defined with the -E option to complete is used.  If a compspec has been defined for that command, the  compspec  is
       used  to  generate  the  list  of  possible  completions for the word.  If the command word is a full pathname, a compspec for the full
       pathname is searched for first.  If no compspec is found for the full pathname, an attempt is made to find a compspec for  the  portion
       following  the final slash.  If those searches do not result in a compspec, any compspec defined with the -D option to complete is used
       as the default.

       Once a compspec has been found, it is used to generate the list of matching words.  If a  compspec  is  not  found,  the  default  bash
       completion as described above under Completing is performed.

       First, the actions specified by the compspec are used.  Only matches which are prefixed by the word being completed are returned.  When
       the -f or -d option is used for filename or directory name completion, the shell variable FIGNORE is used to filter the matches.

       Any completions specified by a pathname expansion pattern to the -G option are generated next.  The words generated by the pattern need
       not match the word being completed.  The GLOBIGNORE shell variable is not used to filter the matches, but the FIGNORE variable is used.

       Next,  the  string specified as the argument to the -W option is considered.  The string is first split using the characters in the IFS
       special variable as delimiters.  Shell quoting is honored.  Each  word  is  then  expanded  using  brace  expansion,  tilde  expansion,
       parameter  and variable expansion, command substitution, and arithmetic expansion, as described above under EXPANSION.  The results are
       split using the rules described above under Word Splitting.  The results of the expansion are prefix-matched  against  the  word  being
       completed, and the matching words become the possible completions.

       After  these  matches  have  been  generated,  any shell function or command specified with the -F and -C options is invoked.  When the
       command or function is invoked, the COMP_LINE, COMP_POINT, COMP_KEY, and COMP_TYPE variables are assigned  values  as  described  above
       under  Shell Variables.  If a shell function is being invoked, the COMP_WORDS and COMP_CWORD variables are also set.  When the function
       or command is invoked, the first argument is the name of the command whose arguments are being completed, the second  argument  is  the
       word  being completed, and the third argument is the word preceding the word being completed on the current command line.  No filtering
       of the generated completions against the word being completed is performed; the function or command has complete freedom in  generating
       the matches.

       Any  function  specified  with  -F  is  invoked first.  The function may use any of the shell facilities, including the compgen builtin
       described below, to generate the matches.  It must put the possible completions in the COMPREPLY array variable.

       Next, any command specified with the -C option is invoked in an environment equivalent to command substitution.  It should print a list
       of completions, one per line, to the standard output.  Backslash may be used to escape a newline, if necessary.

       After  all  of the possible completions are generated, any filter specified with the -X option is applied to the list.  The filter is a
       pattern as used for pathname expansion; a & in the pattern is replaced with the text of the word being completed.  A literal &  may  be
       escaped  with a backslash; the backslash is removed before attempting a match.  Any completion that matches the pattern will be removed
       from the list.  A leading ! negates the pattern; in this case any completion not matching the pattern will be removed.

       Finally, any prefix and suffix specified with the -P and -S options are added to each member of the completion list, and the result  is
       returned to the readline completion code as the list of possible completions.

       If  the  previously-applied  actions do not generate any matches, and the -o dirnames option was supplied to complete when the compspec
       was defined, directory name completion is attempted.

       If the -o plusdirs option was supplied to complete when the compspec was defined,  directory  name  completion  is  attempted  and  any
       matches are added to the results of the other actions.

       By  default,  if a compspec is found, whatever it generates is returned to the completion code as the full set of possible completions.
       The default bash completions are not attempted, and the readline default of filename completion is disabled.   If  the  -o  bashdefault
       option  was supplied to complete when the compspec was defined, the bash default completions are attempted if the compspec generates no
       matches.  If the -o default option was supplied to complete when the compspec  was  defined,  readline's  default  completion  will  be
       performed if the compspec (and, if attempted, the default bash completions) generate no matches.

       When  a  compspec indicates that directory name completion is desired, the programmable completion functions force readline to append a
       slash to completed names which are symbolic links to directories, subject to the  value  of  the  mark-directories  readline  variable,
       regardless of the setting of the mark-symlinked-directories readline variable.

       There  is  some  support for dynamically modifying completions.  This is most useful when used in combination with a default completion
       specified with complete -D.  It's possible for shell functions executed as completion handlers to indicate that  completion  should  be
       retried  by  returning an exit status of 124.  If a shell function returns 124, and changes the compspec associated with the command on
       which completion is being attempted (supplied as the first argument when the function is executed),  programmable  completion  restarts
       from  the beginning, with an attempt to find a new compspec for that command.  This allows a set of completions to be built dynamically
       as completion is attempted, rather than being loaded all at once.

       For instance, assuming that there is a library of compspecs, each kept in a  file  corresponding  to  the  name  of  the  command,  the
       following default completion function would load completions dynamically:

       _completion_loader()
       {
            . "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return 124
       }
       complete -D -F _completion_loader

HISTORY

       When  the  -o  history  option  to  the  set builtin is enabled, the shell provides access to the command history, the list of commands
       previously typed.  The value of the HISTSIZE variable is used as the number of commands to save in a history list.   The  text  of  the
       last  HISTSIZE  commands  (default  500)  is  saved.  The shell stores each command in the history list prior to parameter and variable
       expansion (see EXPANSION above) but after history expansion is performed, subject to the values of the shell variables  HISTIGNORE  and
       HISTCONTROL.

       On  startup,  the history is initialized from the file named by the variable HISTFILE (default ~/.bash_history).  The file named by the
       value of HISTFILE is truncated, if necessary, to contain no more than the number of lines specified by the value of HISTFILESIZE.  When
       the  history  file  is  read,  lines  beginning  with  the history comment character followed immediately by a digit are interpreted as
       timestamps for the preceding history line.  These timestamps are optionally displayed depending on  the  value  of  the  HISTTIMEFORMAT
       variable.   When an interactive shell exits, the last $HISTSIZE lines are copied from the history list to $HISTFILE.  If the histappend
       shell option is enabled (see the description of shopt under SHELL BUILTIN COMMANDS below), the lines are appended to the history  file,
       otherwise  the  history file is overwritten.  If HISTFILE is unset, or if the history file is unwritable, the history is not saved.  If
       the HISTTIMEFORMAT variable is set, time stamps are written to the history file, marked with the history comment character, so they may
       be preserved across shell sessions.  This uses the history comment character to distinguish timestamps from other history lines.  After
       saving the history, the history file is truncated to contain no  more  than  HISTFILESIZE  lines.   If  HISTFILESIZE  is  not  set,  no
       truncation is performed.

       The  builtin  command  fc  (see SHELL BUILTIN COMMANDS below) may be used to list or edit and re-execute a portion of the history list.
       The history builtin may be used to display or modify the history list  and  manipulate  the  history  file.   When  using  command-line
       editing, search commands are available in each editing mode that provide access to the history list.

       The  shell  allows  control  over which commands are saved on the history list.  The HISTCONTROL and HISTIGNORE variables may be set to
       cause the shell to save only a subset of the commands entered.  The cmdhist shell option, if enabled, causes the shell  to  attempt  to
       save  each line of a multi-line command in the same history entry, adding semicolons where necessary to preserve syntactic correctness.
       The lithist shell option causes the shell to save the command with embedded newlines instead of semicolons.  See the description of the
       shopt builtin below under SHELL BUILTIN COMMANDS for information on setting and unsetting shell options.

HISTORY EXPANSION

       The  shell  supports  a  history expansion feature that is similar to the history expansion in csh.  This section describes what syntax
       features are available.  This feature is enabled by default for interactive shells, and can be disabled using the +H option to the  set
       builtin command (see SHELL BUILTIN COMMANDS below).  Non-interactive shells do not perform history expansion by default.

       History expansions introduce words from the history list into the input stream, making it easy to repeat commands, insert the arguments
       to a previous command into the current input line, or fix errors in previous commands quickly.

       History expansion is performed immediately after a complete line is read, before the shell breaks it into words.  It takes place in two
       parts.   The  first  is  to determine which line from the history list to use during substitution.  The second is to select portions of
       that line for inclusion into the current one.  The line selected from the history is the event, and the portions of that line that  are
       acted  upon  are  words.   Various modifiers are available to manipulate the selected words.  The line is broken into words in the same
       fashion as when reading input, so that several metacharacter-separated words surrounded by quotes are  considered  one  word.   History
       expansions  are  introduced by the appearance of the history expansion character, which is ! by default.  Only backslash (\) and single
       quotes can quote the history expansion character.

       Several characters inhibit history expansion if found immediately following the history expansion character, even if  it  is  unquoted:
       space, tab, newline, carriage return, and =.  If the extglob shell option is enabled, ( will also inhibit expansion.

       Several shell options settable with the shopt builtin may be used to tailor the behavior of history expansion.  If the histverify shell
       option is enabled (see the description of the shopt builtin  below),  and  readline  is  being  used,  history  substitutions  are  not
       immediately  passed  to  the  shell  parser.   Instead,  the  expanded  line  is  reloaded into the readline editing buffer for further
       modification.  If readline is being used, and the histreedit shell option is enabled, a failed history substitution  will  be  reloaded
       into  the  readline  editing  buffer  for  correction.   The -p option to the history builtin command may be used to see what a history
       expansion will do before using it.  The -s option to the history builtin may be used to add commands to the end  of  the  history  list
       without actually executing them, so that they are available for subsequent recall.

       The  shell  allows  control  of  the various characters used by the history expansion mechanism (see the description of histchars above
       under Shell Variables).  The shell uses the history comment character to mark history timestamps when writing the history file.

   Event Designators
       An event designator is a reference to a command line entry in the history list.  Unless the reference is absolute, events are  relative
       to the current position in the history list.

       !      Start  a  history substitution, except when followed by a blank, newline, carriage return, = or ( (when the extglob shell option
              is enabled using the shopt builtin).
       !n     Refer to command line n.
       !-n    Refer to the current command minus n.
       !!     Refer to the previous command.  This is a synonym for `!-1'.
       !string
              Refer to the most recent command preceding the current position in the history list starting with string.
       !?string[?]
              Refer to the most recent command preceding the current postition in the history list containing string.  The trailing ?  may  be
              omitted if string is followed immediately by a newline.
       ^string1^string2^
              Quick  substitution.  Repeat the previous command, replacing string1 with string2.  Equivalent to ``!!:s/string1/string2/'' (see
              Modifiers below).
       !#     The entire command line typed so far.

   Word Designators
       Word designators are used to select desired words from the event.  A : separates the event specification from the word designator.   It
       may  be  omitted  if  the  word designator begins with a ^, $, *, -, or %.  Words are numbered from the beginning of the line, with the
       first word being denoted by 0 (zero).  Words are inserted into the current line separated by single spaces.

       0 (zero)
              The zeroth word.  For the shell, this is the command word.
       n      The nth word.
       ^      The first argument.  That is, word 1.
       $      The last argument.
       %      The word matched by the most recent `?string?' search.
       x-y    A range of words; `-y' abbreviates `0-y'.
       *      All of the words but the zeroth.  This is a synonym for `1-$'.  It is not an error to use * if there is just  one  word  in  the
              event; the empty string is returned in that case.
       x*     Abbreviates x-$.
       x-     Abbreviates x-$ like x*, but omits the last word.

       If a word designator is supplied without an event specification, the previous command is used as the event.

   Modifiers
       After the optional word designator, there may appear a sequence of one or more of the following modifiers, each preceded by a `:'.

       h      Remove a trailing file name component, leaving only the head.
       t      Remove all leading file name components, leaving the tail.
       r      Remove a trailing suffix of the form .xxx, leaving the basename.
       e      Remove all but the trailing suffix.
       p      Print the new command but do not execute it.
       q      Quote the substituted words, escaping further substitutions.
       x      Quote the substituted words as with q, but break into words at blanks and newlines.
       s/old/new/
              Substitute new for the first occurrence of old in the event line.  Any delimiter can be used in place of /.  The final delimiter
              is optional if it is the last character of the event line.  The delimiter may be quoted in old and new with a single  backslash.
              If  &  appears  in  new, it is replaced by old.  A single backslash will quote the &.  If old is null, it is set to the last old
              substituted, or, if no previous history substitutions took place, the last string in a !?string[?]  search.
       &      Repeat the previous substitution.
       g      Cause changes to be applied over the entire event line.  This is used in conjunction with `:s' (e.g., `:gs/old/new/')  or  `:&'.
              If  used  with `:s', any delimiter can be used in place of /, and the final delimiter is optional if it is the last character of
              the event line.  An a may be used as a synonym for g.
       G      Apply the following `s' modifier once to each word in the event line.

SHELL BUILTIN COMMANDS

       Unless otherwise noted, each builtin command documented in this section as accepting options preceded by - accepts --  to  signify  the
       end  of  the  options.   The  :, true, false, and test builtins do not accept options and do not treat -- specially.  The exit, logout,
       break, continue, let, and shift builtins accept and process arguments beginning with -  without  requiring  --.   Other  builtins  that
       accept  arguments  but are not specified as accepting options interpret arguments beginning with - as invalid options and require -- to
       prevent this interpretation.
       : [arguments]
              No effect; the command does nothing beyond expanding arguments and performing any specified redirections.  A zero exit  code  is
              returned.

        .  filename [arguments]
       source filename [arguments]
              Read and execute commands from filename in the current shell environment and return the exit status of the last command executed
              from filename.  If filename does not contain a slash, file names in PATH are used to find  the  directory  containing  filename.
              The  file  searched for in PATH need not be executable.  When bash is not in posix mode, the current directory is searched if no
              file is found in PATH.  If the sourcepath option to the shopt builtin command is turned off, the PATH is not searched.   If  any
              arguments  are  supplied,  they become the positional parameters when filename is executed.  Otherwise the positional parameters
              are unchanged.  The return status is the status of the last command exited within the script (0 if no  commands  are  executed),
              and false if filename is not found or cannot be read.

       alias [-p] [name[=value] ...]
              Alias  with no arguments or with the -p option prints the list of aliases in the form alias name=value on standard output.  When
              arguments are supplied, an alias is defined for each name whose value is given.  A trailing space in  value causes the next word
              to  be  checked  for  alias  substitution  when the alias is expanded.  For each name in the argument list for which no value is
              supplied, the name and value of the alias is printed.  Alias returns true unless a name is given for which  no  alias  has  been
              defined.

       bg [jobspec ...]
              Resume  each  suspended job jobspec in the background, as if it had been started with &.  If jobspec is not present, the shell's
              notion of the current job is used.  bg jobspec returns 0 unless run when job control is disabled or, when run with  job  control
              enabled, any specified jobspec was not found or was started without job control.

       bind [-m keymap] [-lpsvPSV]
       bind [-m keymap] [-q function] [-u function] [-r keyseq]
       bind [-m keymap] -f filename
       bind [-m keymap] -x keyseq:shell-command
       bind [-m keymap] keyseq:function-name
       bind readline-command
              Display  current  readline  key  and  function  bindings, bind a key sequence to a readline function or macro, or set a readline
              variable.  Each non-option argument is a command as it would appear in .inputrc, but each binding or command must be passed as a
              separate argument; e.g., '"\C-x\C-r": re-read-init-file'.  Options, if supplied, have the following meanings:
              -m keymap
                     Use  keymap  as the keymap to be affected by the subsequent bindings.  Acceptable keymap names are emacs, emacs-standard,
                     emacs-meta, emacs-ctlx, vi, vi-move, vi-command, and vi-insert.  vi is equivalent to vi-command; emacs is  equivalent  to
                     emacs-standard.
              -l     List the names of all readline functions.
              -p     Display readline function names and bindings in such a way that they can be re-read.
              -P     List current readline function names and bindings.
              -s     Display readline key sequences bound to macros and the strings they output in such a way that they can be re-read.
              -S     Display readline key sequences bound to macros and the strings they output.
              -v     Display readline variable names and values in such a way that they can be re-read.
              -V     List current readline variable names and values.
              -f filename
                     Read key bindings from filename.
              -q function
                     Query about which keys invoke the named function.
              -u function
                     Unbind all keys bound to the named function.
              -r keyseq
                     Remove any current binding for keyseq.
              -x keyseq:shell-command
                     Cause  shell-command  to  be  executed  whenever  keyseq  is entered.  When shell-command is executed, the shell sets the
                     READLINE_LINE variable to the contents of the readline line  buffer  and  the  READLINE_POINT  variable  to  the  current
                     location of the insertion point.  If the executed command changes the value of READLINE_LINE or READLINE_POINT, those new
                     values will be reflected in the editing state.

              The return value is 0 unless an unrecognized option is given or an error occurred.

       break [n]
              Exit from within a for, while, until, or select loop.  If n is specified, break n levels.  n must be ≥ 1.  If n is greater  than
              the  number  of enclosing loops, all enclosing loops are exited.  The return value is 0 unless n is not greater than or equal to
              1.

       builtin shell-builtin [arguments]
              Execute the specified shell builtin, passing it arguments, and return its exit status.  This is useful when defining a  function
              whose  name  is  the same as a shell builtin, retaining the functionality of the builtin within the function.  The cd builtin is
              commonly redefined this way.  The return status is false if shell-builtin is not a shell builtin command.

       caller [expr]
              Returns the context of any active subroutine call (a shell function or a  script  executed  with  the  .  or  source  builtins).
              Without  expr, caller displays the line number and source filename of the current subroutine call.  If a non-negative integer is
              supplied as expr, caller displays the line number, subroutine name, and source  file  corresponding  to  that  position  in  the
              current  execution  call  stack.  This extra information may be used, for example, to print a stack trace.  The current frame is
              frame 0.  The return value is 0 unless the shell is not executing a subroutine call or expr  does  not  correspond  to  a  valid
              position in the call stack.

       cd [-L|[-P [-e]]] [dir]
              Change the current directory to dir.  The variable HOME is the default dir.  The variable CDPATH defines the search path for the
              directory containing dir.  Alternative directory names in CDPATH are separated by a colon (:).  A null directory name in  CDPATH
              is  the same as the current directory, i.e., ``.''.  If dir begins with a slash (/), then CDPATH is not used. The -P option says
              to use the physical directory structure instead of following symbolic links (see also the -P option to the set builtin command);
              the  -L  option  forces  symbolic links to be followed.  If the -e option is supplied with -P, and the current working directory
              cannot be successfully determined after a successful directory change, cd will return an unsuccessful status.  An argument of  -
              is  equivalent  to $OLDPWD.  If a non-empty directory name from CDPATH is used, or if - is the first argument, and the directory
              change is successful, the absolute pathname of the new working directory is written to the standard output.  The return value is
              true if the directory was successfully changed; false otherwise.

       command [-pVv] command [arg ...]
              Run  command  with  args  suppressing  the normal shell function lookup. Only builtin commands or commands found in the PATH are
              executed.  If the -p option is given, the search for command is performed using a default value for PATH that is  guaranteed  to
              find  all  of  the  standard utilities.  If either the -V or -v option is supplied, a description of command is printed.  The -v
              option causes a single word indicating the command or file name used to invoke command to be displayed; the -V option produces a
              more  verbose  description.   If  the  -V or -v option is supplied, the exit status is 0 if command was found, and 1 if not.  If
              neither option is supplied and an error occurred or command cannot be found, the exit status is 127.  Otherwise, the exit status
              of the command builtin is the exit status of command.

       compgen [option] [word]
              Generate possible completion matches for word according to the options, which may be any option accepted by the complete builtin
              with the exception of -p and -r, and write the matches to the standard output.  When using the -F or  -C  options,  the  various
              shell variables set by the programmable completion facilities, while available, will not have useful values.

              The  matches  will  be  generated  in  the  same  way  as if the programmable completion code had generated them directly from a
              completion specification with the same flags.  If word is specified, only those completions matching word will be displayed.

              The return value is true unless an invalid option is supplied, or no matches were generated.

       complete [-abcdefgjksuv] [-o comp-option] [-DE] [-A action] [-G globpat] [-W wordlist] [-F function] [-C command]
              [-X filterpat] [-P prefix] [-S suffix] name [name ...]
       complete -pr [-DE] [name ...]
              Specify how arguments to each name should be completed.  If the -p option is supplied, or if no options are  supplied,  existing
              completion  specifications  are  printed  in  a  way that allows them to be reused as input.  The -r option removes a completion
              specification for each name, or, if no names are supplied, all completion specifications.  The  -D  option  indicates  that  the
              remaining options and actions should apply to the ``default'' command completion; that is, completion attempted on a command for
              which no completion has previously been defined.  The -E option indicates that the remaining options and actions should apply to
              ``empty'' command completion; that is, completion attempted on a blank line.

              The  process of applying these completion specifications when word completion is attempted is described above under Programmable
              Completion.

              Other options, if specified, have the following meanings.  The arguments to the -G, -W, and -X options (and, if  necessary,  the
              -P and -S options) should be quoted to protect them from expansion before the complete builtin is invoked.
              -o comp-option
                      The  comp-option controls several aspects of the compspec's behavior beyond the simple generation of completions.  comp-
                      option may be one of:
                      bashdefault
                              Perform the rest of the default bash completions if the compspec generates no matches.
                      default Use readline's default filename completion if the compspec generates no matches.
                      dirnames
                              Perform directory name completion if the compspec generates no matches.
                      filenames
                              Tell readline that the compspec generates filenames, so it can perform any  filename-specific  processing  (like
                              adding  a slash to directory names, quoting special characters, or suppressing trailing spaces).  Intended to be
                              used with shell functions.
                      nospace Tell readline not to append a space (the default) to words completed at the end of the line.
                      plusdirs
                              After any matches defined by the compspec are generated, directory name completion is attempted and any  matches
                              are added to the results of the other actions.
              -A action
                      The action may be one of the following to generate a list of possible completions:
                      alias   Alias names.  May also be specified as -a.
                      arrayvar
                              Array variable names.
                      binding Readline key binding names.
                      builtin Names of shell builtin commands.  May also be specified as -b.
                      command Command names.  May also be specified as -c.
                      directory
                              Directory names.  May also be specified as -d.
                      disabled
                              Names of disabled shell builtins.
                      enabled Names of enabled shell builtins.
                      export  Names of exported shell variables.  May also be specified as -e.
                      file    File names.  May also be specified as -f.
                      function
                              Names of shell functions.
                      group   Group names.  May also be specified as -g.
                      helptopic
                              Help topics as accepted by the help builtin.
                      hostname
                              Hostnames, as taken from the file specified by the HOSTFILE shell variable.
                      job     Job names, if job control is active.  May also be specified as -j.
                      keyword Shell reserved words.  May also be specified as -k.
                      running Names of running jobs, if job control is active.
                      service Service names.  May also be specified as -s.
                      setopt  Valid arguments for the -o option to the set builtin.
                      shopt   Shell option names as accepted by the shopt builtin.
                      signal  Signal names.
                      stopped Names of stopped jobs, if job control is active.
                      user    User names.  May also be specified as -u.
                      variable
                              Names of all shell variables.  May also be specified as -v.
              -C command
                      command is executed in a subshell environment, and its output is used as the possible completions.
              -F function
                      The  shell  function  function is executed in the current shell environment.  When it finishes, the possible completions
                      are retrieved from the value of the COMPREPLY array variable.
              -G globpat
                      The pathname expansion pattern globpat is expanded to generate the possible completions.
              -P prefix
                      prefix is added at the beginning of each possible completion after all other options have been applied.
              -S suffix
                      suffix is appended to each possible completion after all other options have been applied.
              -W wordlist
                      The wordlist is split using the characters in the IFS special  variable  as  delimiters,  and  each  resultant  word  is
                      expanded.  The possible completions are the members of the resultant list which match the word being completed.
              -X filterpat
                      filterpat  is  a pattern as used for pathname expansion.  It is applied to the list of possible completions generated by
                      the preceding options and arguments, and each completion matching filterpat is removed from the list.  A  leading  !  in
                      filterpat negates the pattern; in this case, any completion not matching filterpat is removed.

              The  return  value  is  true  unless  an  invalid  option  is supplied, an option other than -p or -r is supplied without a name
              argument, an attempt is made to remove a completion specification for a name for which no  specification  exists,  or  an  error
              occurs adding a completion specification.

       compopt [-o option] [-DE] [+o option] [name]
              Modify  completion  options  for  each  name according to the options, or for the currently-executing completion if no names are
              supplied.  If no options are given, display the completion options for each name or the current completion.  The possible values
              of  option  are those valid for the complete builtin described above.  The -D option indicates that the remaining options should
              apply to the ``default'' command completion; that is, completion attempted on a command for which no completion  has  previously
              been  defined.   The  -E  option  indicates  that  the  remaining options should apply to ``empty'' command completion; that is,
              completion attempted on a blank line.

              The return value is true unless an invalid option is supplied, an attempt is made to modify the options for a name for which  no
              completion specification exists, or an output error occurs.

       continue [n]
              Resume  the  next  iteration of the enclosing for, while, until, or select loop.  If n is specified, resume at the nth enclosing
              loop.  n must be ≥ 1.  If n is greater than the number of enclosing loops, the last enclosing loop (the ``top-level''  loop)  is
              resumed.  The return value is 0 unless n is not greater than or equal to 1.

       declare [-aAfFgilrtux] [-p] [name[=value] ...]
       typeset [-aAfFgilrtux] [-p] [name[=value] ...]
              Declare  variables and/or give them attributes.  If no names are given then display the values of variables.  The -p option will
              display the attributes and values of each name.  When -p is used with name arguments, additional options are ignored.   When  -p
              is  supplied  without name arguments, it will display the attributes and values of all variables having the attributes specified
              by the additional options.  If no other options are supplied with -p, declare will display the  attributes  and  values  of  all
              shell  variables.   The  -f option will restrict the display to shell functions.  The -F option inhibits the display of function
              definitions; only the function name and attributes are printed.  If the extdebug shell option is enabled using shopt, the source
              file  name and line number where the function is defined are displayed as well.  The -F option implies -f.  The -g option forces
              variables to be created or modified at the global scope, even when declare is executed in a shell function.  It  is  ignored  in
              all  other  cases.   The  following  options can be used to restrict output to variables with the specified attribute or to give
              variables attributes:
              -a     Each name is an indexed array variable (see Arrays above).
              -A     Each name is an associative array variable (see Arrays above).
              -f     Use function names only.
              -i     The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC EVALUATION  above)  is  performed  when  the
                     variable is assigned a value.
              -l     When  the  variable is assigned a value, all upper-case characters are converted to lower-case.  The upper-case attribute
                     is disabled.
              -r     Make names readonly.  These names cannot then be assigned values by subsequent assignment statements or unset.
              -t     Give each name the trace attribute.  Traced functions inherit the DEBUG and RETURN traps from  the  calling  shell.   The
                     trace attribute has no special meaning for variables.
              -u     When  the  variable is assigned a value, all lower-case characters are converted to upper-case.  The lower-case attribute
                     is disabled.
              -x     Mark names for export to subsequent commands via the environment.

              Using `+' instead of `-' turns off the attribute instead, with the exceptions that +a may  not  be  used  to  destroy  an  array
              variable  and  +r  will  not  remove  the readonly attribute.  When used in a function, makes each name local, as with the local
              command, unless the -g option is supplied, If a variable name is followed by =value, the value of the variable is set to  value.
              The  return value is 0 unless an invalid option is encountered, an attempt is made to define a function using ``-f foo=bar'', an
              attempt is made to assign a value to a readonly variable, an attempt is made to assign a value  to  an  array  variable  without
              using the compound assignment syntax (see Arrays above), one of the names is not a valid shell variable name, an attempt is made
              to turn off readonly status for a readonly variable, an attempt is made to turn off array status for an array  variable,  or  an
              attempt is made to display a non-existent function with -f.

       dirs [+n] [-n] [-clpv]
              Without  options, displays the list of currently remembered directories.  The default display is on a single line with directory
              names separated by spaces.  Directories are added to the list with the pushd command; the popd command removes entries from  the
              list.
              +n     Displays the nth entry counting from the left of the list shown by dirs when invoked without options, starting with zero.
              -n     Displays  the  nth  entry  counting  from the right of the list shown by dirs when invoked without options, starting with
                     zero.
              -c     Clears the directory stack by deleting all of the entries.
              -l     Produces a longer listing; the default listing format uses a tilde to denote the home directory.
              -p     Print the directory stack with one entry per line.
              -v     Print the directory stack with one entry per line, prefixing each entry with its index in the stack.

              The return value is 0 unless an invalid option is supplied or n indexes beyond the end of the directory stack.

       disown [-ar] [-h] [jobspec ...]
              Without options, each jobspec is removed from the table of active jobs.  If jobspec is not present, and neither  -a  nor  -r  is
              supplied, the shell's notion of the current job is used.  If the -h option is given, each jobspec is not removed from the table,
              but is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP.  If no jobspec is present, and  neither  the
              -a nor the -r option is supplied, the current job is used.  If no jobspec is supplied, the -a option means to remove or mark all
              jobs; the -r option without a jobspec argument restricts operation to running jobs.  The return value is 0 unless a jobspec does
              not specify a valid job.

       echo [-neE] [arg ...]
              Output  the  args, separated by spaces, followed by a newline.  The return status is always 0.  If -n is specified, the trailing
              newline is suppressed.  If the -e option is given, interpretation of the following backslash-escaped characters is enabled.  The
              -E  option  disables  the interpretation of these escape characters, even on systems where they are interpreted by default.  The
              xpg_echo shell option may be used to dynamically determine whether or not echo expands these escape characters by default.  echo
              does not interpret -- to mean the end of options.  echo interprets the following escape sequences:
              \a     alert (bell)
              \b     backspace
              \c     suppress further output
              \e
              \E     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \0nnn  the eight-bit character whose value is the octal value nnn (zero to three octal digits)
              \xHH   the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)
              \uHHHH the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHH (one to four hex digits)
              \UHHHHHHHH
                     the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHHHHHH (one to eight hex digits)

       enable [-a] [-dnps] [-f filename] [name ...]
              Enable and disable builtin shell commands.  Disabling a builtin allows a disk command which has the same name as a shell builtin
              to be executed without specifying a full pathname, even though the shell normally searches for builtins  before  disk  commands.
              If  -n  is  used,  each  name is disabled; otherwise, names are enabled.  For example, to use the test binary found via the PATH
              instead of the shell builtin version, run ``enable -n test''.  The -f option means to load the new  builtin  command  name  from
              shared object filename, on systems that support dynamic loading.  The -d option will delete a builtin previously loaded with -f.
              If no name arguments are given, or if the -p option is supplied, a list of shell builtins is  printed.   With  no  other  option
              arguments,  the  list  consists of all enabled shell builtins.  If -n is supplied, only disabled builtins are printed.  If -a is
              supplied, the list printed includes all builtins, with an indication of whether or not each is enabled.  If -s is supplied,  the
              output  is  restricted to the POSIX special builtins.  The return value is 0 unless a name is not a shell builtin or there is an
              error loading a new builtin from a shared object.

       eval [arg ...]
              The args are read and concatenated together into a single command.  This command is then read and executed by the shell, and its
              exit status is returned as the value of eval.  If there are no args, or only null arguments, eval returns 0.

       exec [-cl] [-a name] [command [arguments]]
              If  command is specified, it replaces the shell.  No new process is created.  The arguments become the arguments to command.  If
              the -l option is supplied, the shell places a dash at the beginning of the zeroth argument passed  to  command.   This  is  what
              login(1) does.  The -c option causes command to be executed with an empty environment.  If -a is supplied, the shell passes name
              as the zeroth argument to the executed command.  If command cannot be executed for some reason, a non-interactive  shell  exits,
              unless the shell option execfail is enabled, in which case it returns failure.  An interactive shell returns failure if the file
              cannot be executed.  If command is not specified, any redirections take effect in the current shell, and the return status is 0.
              If there is a redirection error, the return status is 1.

       exit [n]
              Cause  the  shell to exit with a status of n.  If n is omitted, the exit status is that of the last command executed.  A trap on
              EXIT is executed before the shell terminates.

       export [-fn] [name[=word]] ...
       export -p
              The supplied names are marked for automatic export to the environment of subsequently executed commands.  If the  -f  option  is
              given,  the  names  refer  to  functions.   If no names are given, or if the -p option is supplied, a list of all names that are
              exported in this shell is printed.  The -n option causes the export property to be removed from each name.  If a  variable  name
              is  followed by =word, the value of the variable is set to word.  export returns an exit status of 0 unless an invalid option is
              encountered, one of the names is not a valid shell variable name, or -f is supplied with a name that is not a function.

       fc [-e ename] [-lnr] [first] [last]
       fc -s [pat=rep] [cmd]
              Fix Command.  In the first form, a range of commands from first to last is selected from the history list.  First and  last  may
              be specified as a string (to locate the last command beginning with that string) or as a number (an index into the history list,
              where a negative number is used as an offset from the current command number).  If last is  not  specified  it  is  set  to  the
              current  command  for  listing  (so  that  ``fc  -l  -10'' prints the last 10 commands) and to first otherwise.  If first is not
              specified it is set to the previous command for editing and -16 for listing.

              The -n option suppresses the command numbers when listing.  The -r option reverses the order of the commands.  If the -l  option
              is  given,  the  commands  are  listed on standard output.  Otherwise, the editor given by ename is invoked on a file containing
              those commands.  If ename is not given, the value of the FCEDIT variable is used, and the value of EDITOR if FCEDIT is not  set.
              If neither variable is set, vi is used.  When editing is complete, the edited commands are echoed and executed.

              In  the  second  form, command is re-executed after each instance of pat is replaced by rep.  A useful alias to use with this is
              ``r="fc -s"'', so that typing ``r cc'' runs the last command beginning  with  ``cc''  and  typing  ``r''  re-executes  the  last
              command.

              If  the first form is used, the return value is 0 unless an invalid option is encountered or first or last specify history lines
              out of range.  If the -e option is supplied, the return value is the value of the last command executed or failure if  an  error
              occurs  with  the temporary file of commands.  If the second form is used, the return status is that of the command re-executed,
              unless cmd does not specify a valid history line, in which case fc returns failure.

       fg [jobspec]
              Resume jobspec in the foreground, and make it the current job.  If jobspec is not present, the shell's notion of the current job
              is used.  The return value is that of the command placed into the foreground, or failure if run when job control is disabled or,
              when run with job control enabled, if jobspec does not specify a valid job or jobspec specifies a job that was  started  without
              job control.

       getopts optstring name [args]
              getopts  is used by shell procedures to parse positional parameters.  optstring contains the option characters to be recognized;
              if a character is followed by a colon, the option is expected to have an argument, which should be separated from  it  by  white
              space.   The  colon  and question mark characters may not be used as option characters.  Each time it is invoked, getopts places
              the next option in the shell variable name, initializing name if it does not exist, and the index of the  next  argument  to  be
              processed  into  the  variable  OPTIND.   OPTIND  is initialized to 1 each time the shell or a shell script is invoked.  When an
              option requires an argument, getopts places  that  argument  into  the  variable  OPTARG.   The  shell  does  not  reset  OPTIND
              automatically;  it  must  be  manually  reset between multiple calls to getopts within the same shell invocation if a new set of
              parameters is to be used.

              When the end of options is encountered, getopts exits with a return value greater than zero.  OPTIND is set to the index of  the
              first non-option argument, and name is set to ?.

              getopts normally parses the positional parameters, but if more arguments are given in args, getopts parses those instead.

              getopts  can  report  errors  in  two ways.  If the first character of optstring is a colon, silent error reporting is used.  In
              normal operation diagnostic messages are printed when invalid options or missing  option  arguments  are  encountered.   If  the
              variable OPTERR is set to 0, no error messages will be displayed, even if the first character of optstring is not a colon.

              If  an  invalid  option  is  seen, getopts places ? into name and, if not silent, prints an error message and unsets OPTARG.  If
              getopts is silent, the option character found is placed in OPTARG and no diagnostic message is printed.

              If a required argument is not found, and getopts is not silent, a question mark (?) is placed in name, OPTARG is  unset,  and  a
              diagnostic  message  is  printed.   If  getopts  is  silent,  then a colon (:) is placed in name and OPTARG is set to the option
              character found.

              getopts returns true if an option, specified or unspecified, is found.  It returns false if the end of options is encountered or
              an error occurs.

       hash [-lr] [-p filename] [-dt] [name]
              Each  time  hash  is  invoked,  the  full  pathname  of the command name is determined by searching the directories in $PATH and
              remembered.  Any previously-remembered pathname is discarded.  If the -p option is supplied, no path search  is  performed,  and
              filename  is used as the full file name of the command.  The -r option causes the shell to forget all remembered locations.  The
              -d option causes the shell to forget the remembered location of each name.  If the -t option is supplied, the full  pathname  to
              which  each name corresponds is printed.  If multiple name arguments are supplied with -t, the name is printed before the hashed
              full pathname.  The -l option causes output to be displayed in a format that may be reused as input.  If no arguments are given,
              or  if  only  -l  is supplied, information about remembered commands is printed.  The return status is true unless a name is not
              found or an invalid option is supplied.

       help [-dms] [pattern]
              Display helpful information about builtin commands.  If pattern is specified, help gives detailed help on all commands  matching
              pattern; otherwise help for all the builtins and shell control structures is printed.
              -d     Display a short description of each pattern
              -m     Display the description of each pattern in a manpage-like format
              -s     Display only a short usage synopsis for each pattern

              The return status is 0 unless no command matches pattern.

       history [n]
       history -c
       history -d offset
       history -anrw [filename]
       history -p arg [arg ...]
       history -s arg [arg ...]
              With  no options, display the command history list with line numbers.  Lines listed with a * have been modified.  An argument of
              n lists only the last n lines.  If the shell variable HISTTIMEFORMAT is set and not null, it is used  as  a  format  string  for
              strftime(3) to display the time stamp associated with each displayed history entry.  No intervening blank is printed between the
              formatted time stamp and the history line.  If filename is supplied, it is used as the name of the history  file;  if  not,  the
              value of HISTFILE is used.  Options, if supplied, have the following meanings:
              -c     Clear the history list by deleting all the entries.
              -d offset
                     Delete the history entry at position offset.
              -a     Append  the  ``new'' history lines (history lines entered since the beginning of the current bash session) to the history
                     file.
              -n     Read the history lines not already read from the history file into the current history list.  These are lines appended to
                     the history file since the beginning of the current bash session.
              -r     Read the contents of the history file and use them as the current history.
              -w     Write the current history to the history file, overwriting the history file's contents.
              -p     Perform  history  substitution  on  the following args and display the result on the standard output.  Does not store the
                     results in the history list.  Each arg must be quoted to disable normal history expansion.
              -s     Store the args in the history list as a single entry.  The last command in the history list is removed  before  the  args
                     are added.

              If  the  HISTTIMEFORMAT variable is set, the time stamp information associated with each history entry is written to the history
              file, marked with the history comment character.  When the history file is  read,  lines  beginning  with  the  history  comment
              character  followed  immediately  by a digit are interpreted as timestamps for the previous history line.  The return value is 0
              unless an invalid option is encountered, an error occurs while reading or  writing  the  history  file,  an  invalid  offset  is
              supplied as an argument to -d, or the history expansion supplied as an argument to -p fails.

       jobs [-lnprs] [ jobspec ... ]
       jobs -x command [ args ... ]
              The first form lists the active jobs.  The options have the following meanings:
              -l     List process IDs in addition to the normal information.
              -n     Display information only about jobs that have changed status since the user was last notified of their status.
              -p     List only the process ID of the job's process group leader.
              -r     Restrict output to running jobs.
              -s     Restrict output to stopped jobs.

              If  jobspec  is  given,  output is restricted to information about that job.  The return status is 0 unless an invalid option is
              encountered or an invalid jobspec is supplied.

              If the -x option is supplied, jobs replaces any jobspec found in command or args with the corresponding process  group  ID,  and
              executes command passing it args, returning its exit status.

       kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
       kill -l [sigspec | exit_status]
              Send  the  signal  named  by  sigspec  or signum to the processes named by pid or jobspec.  sigspec is either a case-insensitive
              signal name such as SIGKILL (with or without the SIG prefix) or a signal number; signum is a signal number.  If sigspec  is  not
              present,  then  SIGTERM  is assumed.  An argument of -l lists the signal names.  If any arguments are supplied when -l is given,
              the names of the signals corresponding to the arguments are listed, and the return status is 0.  The exit_status argument to  -l
              is  a  number specifying either a signal number or the exit status of a process terminated by a signal.  kill returns true if at
              least one signal was successfully sent, or false if an error occurs or an invalid option is encountered.

       let arg [arg ...]
              Each arg is an arithmetic expression to be evaluated (see ARITHMETIC EVALUATION above).  If the last arg  evaluates  to  0,  let
              returns 1; 0 is returned otherwise.

       local [option] [name[=value] ...]
              For each argument, a local variable named name is created, and assigned value.  The option can be any of the options accepted by
              declare.  When local is used within a function, it causes the variable name to have a visible scope restricted to that  function
              and its children.  With no operands, local writes a list of local variables to the standard output.  It is an error to use local
              when not within a function.  The return status is 0 unless local is used outside a function, an invalid  name  is  supplied,  or
              name is a readonly variable.

       logout Exit a login shell.

       mapfile [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
       readarray [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
              Read  lines  from  the  standard  input  into  the  indexed array variable array, or from file descriptor fd if the -u option is
              supplied.  The variable MAPFILE is the default array.  Options, if supplied, have the following meanings:
              -n     Copy at most count lines.  If count is 0, all lines are copied.
              -O     Begin assigning to array at index origin.  The default index is 0.
              -s     Discard the first count lines read.
              -t     Remove a trailing newline from each line read.
              -u     Read lines from file descriptor fd instead of the standard input.
              -C     Evaluate callback each time quantum lines are read.  The -c option specifies quantum.
              -c     Specify the number of lines read between each call to callback.

              If -C is specified without -c, the default quantum is 5000.  When callback is evaluated, it is supplied the index  of  the  next
              array  element  to be assigned and the line to be assigned to that element as additional arguments.  callback is evaluated after
              the line is read but before the array element is assigned.

              If not supplied with an explicit origin, mapfile will clear array before assigning to it.

              mapfile returns successfully unless an invalid option or option argument is supplied, array is invalid or  unassignable,  or  if
              array is not an indexed array.

       popd [-n] [+n] [-n]
              Removes entries from the directory stack.  With no arguments, removes the top directory from the stack, and performs a cd to the
              new top directory.  Arguments, if supplied, have the following meanings:
              -n     Suppresses the normal change of directory  when  removing  directories  from  the  stack,  so  that  only  the  stack  is
                     manipulated.
              +n     Removes  the  nth  entry  counting from the left of the list shown by dirs, starting with zero.  For example: ``popd +0''
                     removes the first directory, ``popd +1'' the second.
              -n     Removes the nth entry counting from the right of the list shown by dirs, starting with zero.  For  example:  ``popd  -0''
                     removes the last directory, ``popd -1'' the next to last.

              If  the  popd  command is successful, a dirs is performed as well, and the return status is 0.  popd returns false if an invalid
              option is encountered, the directory stack is empty, a non-existent directory stack entry is specified, or the directory  change
              fails.

       printf [-v var] format [arguments]
              Write  the  formatted  arguments  to the standard output under the control of the format.  The -v option causes the output to be
              assigned to the variable var rather than being printed to the standard output.

              The format is a character string which contains three types of objects: plain characters, which are simply  copied  to  standard
              output,  character  escape  sequences, which are converted and copied to the standard output, and format specifications, each of
              which causes printing of the next successive argument.  In addition to the  standard  printf(1)  format  specifications,  printf
              interprets the following extensions:
              %b     causes  printf  to  expand  backslash  escape  sequences in the corresponding argument (except that \c terminates output,
                     backslashes in \', \", and \? are not removed, and octal escapes beginning with \0 may contain up to four digits).
              %q     causes printf to output the corresponding argument in a format that can be reused as shell input.
              %(datefmt)T
                     causes printf to output the date-time string resulting from using datefmt  as  a  format  string  for  strftime(3).   The
                     corresponding argument is an integer representing the number of seconds since the epoch.  Two special argument values may
                     be used: -1 represents the current time, and -2 represents the time the shell was invoked.

              Arguments to non-string format specifiers are treated as C constants, except that a leading plus or minus sign is  allowed,  and
              if the leading character is a single or double quote, the value is the ASCII value of the following character.

              The format is reused as necessary to consume all of the arguments.  If the format requires more arguments than are supplied, the
              extra format specifications behave as if a zero value or null string, as appropriate, had been supplied.  The  return  value  is
              zero on success, non-zero on failure.

       pushd [-n] [+n] [-n]
       pushd [-n] [dir]
              Adds  a  directory  to the top of the directory stack, or rotates the stack, making the new top of the stack the current working
              directory.  With no arguments, exchanges the top two directories and returns 0, unless the directory stack is empty.  Arguments,
              if supplied, have the following meanings:
              -n     Suppresses the normal change of directory when adding directories to the stack, so that only the stack is manipulated.
              +n     Rotates  the stack so that the nth directory (counting from the left of the list shown by dirs, starting with zero) is at
                     the top.
              -n     Rotates the stack so that the nth directory (counting from the right of the list shown by dirs, starting with zero) is at
                     the top.
              dir    Adds dir to the directory stack at the top, making it the new current working directory.

              If  the  pushd  command is successful, a dirs is performed as well.  If the first form is used, pushd returns 0 unless the cd to
              dir fails.  With the second form, pushd returns 0 unless the directory stack is empty, a non-existent directory stack element is
              specified, or the directory change to the specified new current directory fails.

       pwd [-LP]
              Print  the absolute pathname of the current working directory.  The pathname printed contains no symbolic links if the -P option
              is supplied or the -o physical option to the set builtin command is enabled.  If the -L option is used, the pathname printed may
              contain  symbolic  links.   The  return status is 0 unless an error occurs while reading the name of the current directory or an
              invalid option is supplied.

       read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t timeout] [-u fd] [name ...]
              One line is read from the standard input, or from the file descriptor fd supplied as an argument to the -u option, and the first
              word  is  assigned  to  the first name, the second word to the second name, and so on, with leftover words and their intervening
              separators assigned to the last name.  If there are fewer words read from the input stream than names, the remaining  names  are
              assigned empty values.  The characters in IFS are used to split the line into words.  The backslash character (\) may be used to
              remove any special meaning for the next character read and for line continuation.  Options,  if  supplied,  have  the  following
              meanings:
              -a aname
                     The  words  are assigned to sequential indices of the array variable aname, starting at 0.  aname is unset before any new
                     values are assigned.  Other name arguments are ignored.
              -d delim
                     The first character of delim is used to terminate the input line, rather than newline.
              -e     If the standard input is coming from a terminal, readline (see READLINE above) is used to obtain the line.  Readline uses
                     the current (or default, if line editing was not previously active) editing settings.
              -i text
                     If readline is being used to read the line, text is placed into the editing buffer before editing begins.
              -n nchars
                     read  returns  after reading nchars characters rather than waiting for a complete line of input, but honor a delimiter if
                     fewer than nchars characters are read before the delimiter.
              -N nchars
                     read returns after reading exactly nchars characters rather than waiting for a complete line  of  input,  unless  EOF  is
                     encountered  or read times out.  Delimiter characters encountered in the input are not treated specially and do not cause
                     read to return until nchars characters are read.
              -p prompt
                     Display prompt on standard error, without a trailing newline, before  attempting  to  read  any  input.   The  prompt  is
                     displayed only if input is coming from a terminal.
              -r     Backslash  does  not  act  as an escape character.  The backslash is considered to be part of the line.  In particular, a
                     backslash-newline pair may not be used as a line continuation.
              -s     Silent mode.  If input is coming from a terminal, characters are not echoed.
              -t timeout
                     Cause read to time out and return failure if a complete line of input is not read within timeout seconds.  timeout may be
                     a decimal number with a fractional portion following the decimal point.  This option is only effective if read is reading
                     input from a terminal, pipe, or other special file; it has no effect when reading from regular files.  If timeout  is  0,
                     read  returns  success  if  input  is  available on the specified file descriptor, failure otherwise.  The exit status is
                     greater than 128 if the timeout is exceeded.
              -u fd  Read input from file descriptor fd.

              If no names are supplied, the line read is assigned to the variable REPLY.  The return  code  is  zero,  unless  end-of-file  is
              encountered,  read  times  out (in which case the return code is greater than 128), or an invalid file descriptor is supplied as
              the argument to -u.

       readonly [-aAf] [-p] [name[=word] ...]
              The given names are marked readonly; the values of these names may not be changed by subsequent assignment.  If the -f option is
              supplied,  the functions corresponding to the names are so marked.  The -a option restricts the variables to indexed arrays; the
              -A option restricts the variables to associative arrays.  If both options  are  supplied,  -A  takes  precedence.   If  no  name
              arguments are given, or if the -p option is supplied, a list of all readonly names is printed.  The other options may be used to
              restrict the output to a subset of the set of readonly names.  The -p option causes output to be displayed in a format that  may
              be  reused as input.  If a variable name is followed by =word, the value of the variable is set to word.  The return status is 0
              unless an invalid option is encountered, one of the names is not a valid shell variable name, or -f is supplied with a name that
              is not a function.

       return [n]
              Causes  a function to exit with the return value specified by n.  If n is omitted, the return status is that of the last command
              executed in the function body.  If used outside a function, but during execution of a script by  the  .   (source)  command,  it
              causes  the  shell  to stop executing that script and return either n or the exit status of the last command executed within the
              script as the exit status of the script.  If used outside a function and not during execution of  a  script  by  .,  the  return
              status is false.  Any command associated with the RETURN trap is executed before execution resumes after the function or script.

       set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
              Without  options, the name and value of each shell variable are displayed in a format that can be reused as input for setting or
              resetting the currently-set variables.  Read-only variables cannot be reset.  In posix mode, only shell  variables  are  listed.
              The  output  is  sorted  according  to the current locale.  When options are specified, they set or unset shell attributes.  Any
              arguments remaining after option processing are treated as values for the positional parameters and are assigned, in  order,  to
              $1, $2, ...  $n.  Options, if specified, have the following meanings:
              -a      Automatically  mark  variables  and  functions which are modified or created for export to the environment of subsequent
                      commands.
              -b      Report the status of terminated background jobs immediately, rather than  before  the  next  primary  prompt.   This  is
                      effective only when job control is enabled.
              -e      Exit  immediately  if  a  pipeline  (which  may  consist  of  a  single simple command),  a subshell command enclosed in
                      parentheses, or one of the commands executed as part of a command list enclosed by  braces  (see  SHELL  GRAMMAR  above)
                      exits with a non-zero status.  The shell does not exit if the command that fails is part of the command list immediately
                      following a while or until keyword, part of the test following the if or  elif  reserved  words,  part  of  any  command
                      executed  in a && or || list except the command following the final && or ||, any command in a pipeline but the last, or
                      if the command's return value is being inverted with !.  A trap on ERR, if set, is  executed  before  the  shell  exits.
                      This option applies to the shell environment and each subshell environment separately (see COMMAND EXECUTION ENVIRONMENT
                      above), and may cause subshells to exit before executing all the commands in the subshell.
              -f      Disable pathname expansion.
              -h      Remember the location of commands as they are looked up for execution.  This is enabled by default.
              -k      All arguments in the form of assignment statements are placed in the environment for a  command,  not  just  those  that
                      precede the command name.
              -m      Monitor  mode.   Job control is enabled.  This option is on by default for interactive shells on systems that support it
                      (see JOB CONTROL above).  Background processes run in a separate process group and a line containing their  exit  status
                      is printed upon their completion.
              -n      Read  commands but do not execute them.  This may be used to check a shell script for syntax errors.  This is ignored by
                      interactive shells.
              -o option-name
                      The option-name can be one of the following:
                      allexport
                              Same as -a.
                      braceexpand
                              Same as -B.
                      emacs   Use an emacs-style command line editing interface.  This is enabled by default when the  shell  is  interactive,
                              unless  the shell is started with the --noediting option.  This also affects the editing interface used for read
                              -e.
                      errexit Same as -e.
                      errtrace
                              Same as -E.
                      functrace
                              Same as -T.
                      hashall Same as -h.
                      histexpand
                              Same as -H.
                      history Enable command history, as described above under HISTORY.  This option is on by default in interactive shells.
                      ignoreeof
                              The effect is as if the shell command ``IGNOREEOF=10'' had been executed (see Shell Variables above).
                      keyword Same as -k.
                      monitor Same as -m.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.
                      nolog   Currently ignored.
                      notify  Same as -b.
                      nounset Same as -u.
                      onecmd  Same as -t.
                      physical
                              Same as -P.
                      pipefail
                              If set, the return value of a pipeline is the value of the last (rightmost) command  to  exit  with  a  non-zero
                              status, or zero if all commands in the pipeline exit successfully.  This option is disabled by default.
                      posix   Change  the  behavior  of bash where the default operation differs from the POSIX standard to match the standard
                              (posix mode).
                      privileged
                              Same as -p.
                      verbose Same as -v.
                      vi      Use a vi-style command line editing interface.  This also affects the editing interface used for read -e.
                      xtrace  Same as -x.
                      If -o is supplied with no option-name, the values of the current options  are  printed.   If  +o  is  supplied  with  no
                      option-name, a series of set commands to recreate the current option settings is displayed on the standard output.
              -p      Turn  on  privileged  mode.   In  this  mode,  the  $ENV  and $BASH_ENV files are not processed, shell functions are not
                      inherited from the environment, and the SHELLOPTS, BASHOPTS, CDPATH, and GLOBIGNORE variables, if  they  appear  in  the
                      environment, are ignored.  If the shell is started with the effective user (group) id not equal to the real user (group)
                      id, and the -p option is not supplied, these actions are taken and the effective user id is set to the real user id.  If
                      the  -p option is supplied at startup, the effective user id is not reset.  Turning this option off causes the effective
                      user and group ids to be set to the real user and group ids.
              -t      Exit after reading and executing one command.
              -u      Treat unset variables and parameters other than the special parameters "@" and "*" as an error when performing parameter
                      expansion.   If expansion is attempted on an unset variable or parameter, the shell prints an error message, and, if not
                      interactive, exits with a non-zero status.
              -v      Print shell input lines as they are read.
              -x      After expanding each simple command, for command, case command, select command, or arithmetic for command,  display  the
                      expanded value of PS4, followed by the command and its expanded arguments or associated word list.
              -B      The shell performs brace expansion (see Brace Expansion above).  This is on by default.
              -C      If  set,  bash does not overwrite an existing file with the >, >&, and <> redirection operators.  This may be overridden
                      when creating output files by using the redirection operator >| instead of >.
              -E      If set, any trap on ERR is inherited by shell functions, command substitutions, and  commands  executed  in  a  subshell
                      environment.  The ERR trap is normally not inherited in such cases.
              -H      Enable !  style history substitution.  This option is on by default when the shell is interactive.
              -P      If  set,  the  shell  does  not follow symbolic links when executing commands such as cd that change the current working
                      directory.  It uses the physical directory structure instead.  By default, bash follows the logical chain of directories
                      when performing commands which change the current directory.
              -T      If  set, any traps on DEBUG and RETURN are inherited by shell functions, command substitutions, and commands executed in
                      a subshell environment.  The DEBUG and RETURN traps are normally not inherited in such cases.
              --      If no arguments follow this option, then the positional parameters are unset.  Otherwise, the positional parameters  are
                      set to the args, even if some of them begin with a -.
              -       Signal  the end of options, cause all remaining args to be assigned to the positional parameters.  The -x and -v options
                      are turned off.  If there are no args, the positional parameters remain unchanged.

              The options are off by default unless otherwise noted.  Using + rather than - causes  these  options  to  be  turned  off.   The
              options  can  also be specified as arguments to an invocation of the shell.  The current set of options may be found in $-.  The
              return status is always true unless an invalid option is encountered.

       shift [n]
              The positional parameters from n+1 ... are renamed to $1 ....  Parameters represented by the  numbers  $#  down  to  $#-n+1  are
              unset.   n must be a non-negative number less than or equal to $#.  If n is 0, no parameters are changed.  If n is not given, it
              is assumed to be 1.  If n is greater than $#, the positional parameters are not changed.  The return status is greater than zero
              if n is greater than $# or less than zero; otherwise 0.

       shopt [-pqsu] [-o] [optname ...]
              Toggle  the  values  of  variables  controlling  optional shell behavior.  With no options, or with the -p option, a list of all
              settable options is displayed, with an indication of whether or not each is set.  The -p option causes output to be displayed in
              a form that may be reused as input.  Other options have the following meanings:
              -s     Enable (set) each optname.
              -u     Disable (unset) each optname.
              -q     Suppresses  normal  output  (quiet  mode);  the return status indicates whether the optname is set or unset.  If multiple
                     optname arguments are given with -q, the return status is zero if all optnames are enabled; non-zero otherwise.
              -o     Restricts the values of optname to be those defined for the -o option to the set builtin.

              If either -s or -u is used with no optname arguments, the  display  is  limited  to  those  options  which  are  set  or  unset,
              respectively.  Unless otherwise noted, the shopt options are disabled (unset) by default.

              The  return  status  when  listing  options  is zero if all optnames are enabled, non-zero otherwise.  When setting or unsetting
              options, the return status is zero unless an optname is not a valid shell option.

              The list of shopt options is:

              autocd  If set, a command name that is the name of a directory is executed as if it were the argument to the cd  command.   This
                      option is only used by interactive shells.
              cdable_vars
                      If  set,  an  argument  to  the cd builtin command that is not a directory is assumed to be the name of a variable whose
                      value is the directory to change to.
              cdspell If set, minor errors in the spelling of a directory component in a cd command will be corrected.  The errors checked for
                      are  transposed  characters,  a  missing character, and one character too many.  If a correction is found, the corrected
                      file name is printed, and the command proceeds.  This option is only used by interactive shells.
              checkhash
                      If set, bash checks that a command found in the hash table exists before trying to execute it.  If a hashed  command  no
                      longer exists, a normal path search is performed.
              checkjobs
                      If  set,  bash  lists  the  status of any stopped and running jobs before exiting an interactive shell.  If any jobs are
                      running, this causes the exit to be deferred until a second exit is attempted without an intervening  command  (see  JOB
                      CONTROL above).  The shell always postpones exiting if any jobs are stopped.
              checkwinsize
                      If set, bash checks the window size after each command and, if necessary, updates the values of LINES and COLUMNS.
              cmdhist If  set,  bash  attempts  to  save all lines of a multiple-line command in the same history entry.  This allows easy re-
                      editing of multi-line commands.
              compat31
                      If set, bash changes its behavior to that of version 3.1  with  respect  to  quoted  arguments  to  the  [[  conditional
                      command's =~ operator.
              compat32
                      If  set,  bash  changes its behavior to that of version 3.2 with respect to locale-specific string comparison when using
                      the [[ conditional command's < and > operators.  Bash versions prior to bash-4.1  use  ASCII  collation  and  strcmp(3);
                      bash-4.1 and later use the current locale's collation sequence and strcoll(3).
              compat40
                      If  set,  bash  changes its behavior to that of version 4.0 with respect to locale-specific string comparison when using
                      the [[ conditional command's < and > operators (see previous item) and the effect of interrupting a command list.
              compat41
                      If set, bash, when in posix mode, treats a single quote in a double-quoted parameter expansion as a  special  character.
                      The  single quotes must match (an even number) and the characters between the single quotes are considered quoted.  This
                      is the behavior of posix mode through version 4.1.  The default bash behavior remains as in previous versions.
              direxpand
                      If set, bash replaces directory names with the results of word expansion  when  performing  filename  completion.   This
                      changes the contents of the readline editing buffer.  If not set, bash attempts to preserve what the user typed.
              dirspell
                      If  set,  bash  attempts  spelling  correction on directory names during word completion if the directory name initially
                      supplied does not exist.
              dotglob If set, bash includes filenames beginning with a `.' in the results of pathname expansion.
              execfail
                      If set, a non-interactive shell will not exit if it cannot execute the file specified as an argument to the exec builtin
                      command.  An interactive shell does not exit if exec fails.
              expand_aliases
                      If  set,  aliases  are  expanded  as  described  above under ALIASES.  This option is enabled by default for interactive
                      shells.
              extdebug
                      If set, behavior intended for use by debuggers is enabled:
                      1.     The -F option to the declare builtin displays the source file name and line number corresponding to each function
                             name supplied as an argument.
                      2.     If the command run by the DEBUG trap returns a non-zero value, the next command is skipped and not executed.
                      3.     If  the  command  run by the DEBUG trap returns a value of 2, and the shell is executing in a subroutine (a shell
                             function or a shell script executed by the . or source builtins), a call to return is simulated.
                      4.     BASH_ARGC and BASH_ARGV are updated as described in their descriptions above.
                      5.     Function tracing is enabled:  command substitution, shell functions, and  subshells  invoked  with  (  command  )
                             inherit the DEBUG and RETURN traps.
                      6.     Error  tracing is enabled:  command substitution, shell functions, and subshells invoked with ( command ) inherit
                             the ERR trap.
              extglob If set, the extended pattern matching features described above under Pathname Expansion are enabled.
              extquote
                      If set, $'string' and $"string" quoting is performed within ${parameter} expansions enclosed  in  double  quotes.   This
                      option is enabled by default.
              failglob
                      If set, patterns which fail to match filenames during pathname expansion result in an expansion error.
              force_fignore
                      If  set,  the suffixes specified by the FIGNORE shell variable cause words to be ignored when performing word completion
                      even if the ignored words are the only possible completions.  See SHELL VARIABLES above for a  description  of  FIGNORE.
                      This option is enabled by default.
              globstar
                      If  set,  the  pattern  **  used  in  a pathname expansion context will match all files and zero or more directories and
                      subdirectories.  If the pattern is followed by a /, only directories and subdirectories match.
              gnu_errfmt
                      If set, shell error messages are written in the standard GNU error message format.
              histappend
                      If set, the history list is appended to the file named by the value of the  HISTFILE  variable  when  the  shell  exits,
                      rather than overwriting the file.
              histreedit
                      If set, and readline is being used, a user is given the opportunity to re-edit a failed history substitution.
              histverify
                      If  set, and readline is being used, the results of history substitution are not immediately passed to the shell parser.
                      Instead, the resulting line is loaded into the readline editing buffer, allowing further modification.
              hostcomplete
                      If set, and readline is being used, bash will attempt to perform hostname completion when a word containing a @ is being
                      completed (see Completing under READLINE above).  This is enabled by default.
              huponexit
                      If set, bash will send SIGHUP to all jobs when an interactive login shell exits.
              interactive_comments
                      If  set,  allow a word beginning with # to cause that word and all remaining characters on that line to be ignored in an
                      interactive shell (see COMMENTS above).  This option is enabled by default.
              lastpipe
                      If set, and job control is not active, the shell runs the last command of a pipeline not executed in the  background  in
                      the current shell environment.
              lithist If  set,  and  the cmdhist option is enabled, multi-line commands are saved to the history with embedded newlines rather
                      than using semicolon separators where possible.
              login_shell
                      The shell sets this option if it is started as a login shell (see INVOCATION above).  The value may not be changed.
              mailwarn
                      If set, and a file that bash is checking for mail has been accessed since the last time  it  was  checked,  the  message
                      ``The mail in mailfile has been read'' is displayed.
              no_empty_cmd_completion
                      If set, and readline is being used, bash will not attempt to search the PATH for possible completions when completion is
                      attempted on an empty line.
              nocaseglob
                      If set, bash matches filenames in a case-insensitive fashion when performing pathname expansion (see Pathname  Expansion
                      above).
              nocasematch
                      If  set,  bash  matches  patterns  in  a  case-insensitive  fashion  when performing matching while executing case or [[
                      conditional commands.
              nullglob
                      If set, bash allows patterns which match no files (see Pathname Expansion above) to expand to a null string, rather than
                      themselves.
              progcomp
                      If  set, the programmable completion facilities (see Programmable Completion above) are enabled.  This option is enabled
                      by default.
              promptvars
                      If set, prompt strings undergo parameter expansion, command substitution, arithmetic expansion, and quote removal  after
                      being expanded as described in PROMPTING above.  This option is enabled by default.
              restricted_shell
                      The  shell  sets  this  option  if  it is started in restricted mode (see RESTRICTED SHELL below).  The value may not be
                      changed.  This is not reset when the startup files are executed, allowing the startup files to discover whether or not a
                      shell is restricted.
              shift_verbose
                      If set, the shift builtin prints an error message when the shift count exceeds the number of positional parameters.
              sourcepath
                      If set, the source (.) builtin uses the value of PATH to find the directory containing the file supplied as an argument.
                      This option is enabled by default.
              xpg_echo
                      If set, the echo builtin expands backslash-escape sequences by default.

       suspend [-f]
              Suspend the execution of this shell until it receives a SIGCONT signal.  A login shell cannot be suspended; the -f option can be
              used  to  override  this  and  force  the  suspension.   The  return status is 0 unless the shell is a login shell and -f is not
              supplied, or if job control is not enabled.

       test expr
       [ expr ]
              Return a status of 0 or 1 depending on the evaluation of the conditional expression expr.  Each operator and operand must  be  a
              separate  argument.   Expressions  are  composed  of the primaries described above under CONDITIONAL EXPRESSIONS.  test does not
              accept any options, nor does it accept and ignore an argument of -- as signifying the end of options.

              Expressions may be combined using the following operators, listed in decreasing order of precedence.  The evaluation depends  on
              the number of arguments; see below.  Operator precedence is used when there are five or more arguments.
              ! expr True if expr is false.
              ( expr )
                     Returns the value of expr.  This may be used to override the normal precedence of operators.
              expr1 -a expr2
                     True if both expr1 and expr2 are true.
              expr1 -o expr2
                     True if either expr1 or expr2 is true.

              test and [ evaluate conditional expressions using a set of rules based on the number of arguments.

              0 arguments
                     The expression is false.
              1 argument
                     The expression is true if and only if the argument is not null.
              2 arguments
                     If  the first argument is !, the expression is true if and only if the second argument is null.  If the first argument is
                     one of the unary conditional operators listed above under CONDITIONAL EXPRESSIONS, the expression is true  if  the  unary
                     test is true.  If the first argument is not a valid unary conditional operator, the expression is false.
              3 arguments
                     The  following  conditions  are  applied  in  the  order listed.  If the second argument is one of the binary conditional
                     operators listed above under CONDITIONAL EXPRESSIONS, the result of the expression is the result of the binary test using
                     the  first and third arguments as operands.  The -a and -o operators are considered binary operators when there are three
                     arguments.  If the first argument is !, the value is the negation of the two-argument test using  the  second  and  third
                     arguments.   If  the first argument is exactly ( and the third argument is exactly ), the result is the one-argument test
                     of the second argument.  Otherwise, the expression is false.
              4 arguments
                     If the first argument is !, the result is the negation  of  the  three-argument  expression  composed  of  the  remaining
                     arguments.  Otherwise, the expression is parsed and evaluated according to precedence using the rules listed above.
              5 or more arguments
                     The expression is parsed and evaluated according to precedence using the rules listed above.

              When used with test or [, the < and > operators sort lexicographically using ASCII ordering.

       times  Print the accumulated user and system times for the shell and for processes run from the shell.  The return status is 0.

       trap [-lp] [[arg] sigspec ...]
              The  command  arg is to be read and executed when the shell receives signal(s) sigspec.  If arg is absent (and there is a single
              sigspec) or -, each specified signal is reset to its original disposition (the value it had upon entrance to the shell).  If arg
              is  the  null string the signal specified by each sigspec is ignored by the shell and by the commands it invokes.  If arg is not
              present and -p has been supplied, then the trap commands associated with each  sigspec  are  displayed.   If  no  arguments  are
              supplied  or  if only -p is given, trap prints the list of commands associated with each signal.  The -l option causes the shell
              to print a list of signal names and their corresponding numbers.  Each sigspec is either a signal name defined in <signal.h>, or
              a signal number.  Signal names are case insensitive and the SIG prefix is optional.

              If a sigspec is EXIT (0) the command arg is executed on exit from the shell.  If a sigspec is DEBUG, the command arg is executed
              before every simple command, for command, case command, select command, every arithmetic  for  command,  and  before  the  first
              command  executes  in  a shell function (see SHELL GRAMMAR above).  Refer to the description of the extdebug option to the shopt
              builtin for details of its effect on the DEBUG trap.  If a sigspec is RETURN, the command arg is  executed  each  time  a  shell
              function or a script executed with the . or source builtins finishes executing.

              If  a sigspec is ERR, the command arg is executed whenever a simple command has a non-zero exit status, subject to the following
              conditions.  The ERR trap is not executed if the failed command is part of the command list immediately  following  a  while  or
              until  keyword,  part  of the test in an if statement, part of a command executed in a && or || list, or if the command's return
              value is being inverted via !.  These are the same conditions obeyed by the errexit option.

              Signals ignored upon entry to the shell cannot be trapped or reset.  Trapped signals that are not being  ignored  are  reset  to
              their  original  values in a subshell or subshell environment when one is created.  The return status is false if any sigspec is
              invalid; otherwise trap returns true.

       type [-aftpP] name [name ...]
              With no options, indicate how each name would be interpreted if used as a command name.  If the -t option is used, type prints a
              string  which  is one of alias, keyword, function, builtin, or file if name is an alias, shell reserved word, function, builtin,
              or disk file, respectively.  If the name is not found, then nothing is printed, and an exit status of false is returned.  If the
              -p  option  is  used,  type  either returns the name of the disk file that would be executed if name were specified as a command
              name, or nothing if ``type -t name'' would not return file.  The -P option forces a PATH search for each name, even if ``type -t
              name''  would  not return file.  If a command is hashed, -p and -P print the hashed value, not necessarily the file that appears
              first in PATH.  If the -a option is used, type prints all of the places that contain an executable named  name.   This  includes
              aliases  and functions, if and only if the -p option is not also used.  The table of hashed commands is not consulted when using
              -a.  The -f option suppresses shell function lookup, as with the command builtin.  type returns true if all of the arguments are
              found, false if any are not found.

       ulimit [-HSTabcdefilmnpqrstuvx [limit]]
              Provides  control  over the resources available to the shell and to processes started by it, on systems that allow such control.
              The -H and -S options specify that the hard or soft limit is set for the given resource.  A hard limit cannot be increased by  a
              non-root  user  once  it  is  set;  a  soft  limit  may be increased up to the value of the hard limit.  If neither -H nor -S is
              specified, both the soft and hard limits are set.  The value of limit can be a number in the unit specified for the resource  or
              one  of  the  special  values  hard,  soft, or unlimited, which stand for the current hard limit, the current soft limit, and no
              limit, respectively.  If limit is omitted, the current value of the soft limit of the resource is printed, unless the -H  option
              is  given.   When  more than one resource is specified, the limit name and unit are printed before the value.  Other options are
              interpreted as follows:
              -a     All current limits are reported
              -b     The maximum socket buffer size
              -c     The maximum size of core files created
              -d     The maximum size of a process's data segment
              -e     The maximum scheduling priority ("nice")
              -f     The maximum size of files written by the shell and its children
              -i     The maximum number of pending signals
              -l     The maximum size that may be locked into memory
              -m     The maximum resident set size (many systems do not honor this limit)
              -n     The maximum number of open file descriptors (most systems do not allow this value to be set)
              -p     The pipe size in 512-byte blocks (this may not be set)
              -q     The maximum number of bytes in POSIX message queues
              -r     The maximum real-time scheduling priority
              -s     The maximum stack size
              -t     The maximum amount of cpu time in seconds
              -u     The maximum number of processes available to a single user
              -v     The maximum amount of virtual memory available to the shell and, on some systems, to its children
              -x     The maximum number of file locks
              -T     The maximum number of threads

              If limit is given, it is the new value of the specified resource (the -a option is display only).  If no option is  given,  then
              -f  is  assumed.   Values  are  in  1024-byte  increments, except for -t, which is in seconds, -p, which is in units of 512-byte
              blocks, and -T, -b, -n, and -u, which are unscaled values.  The return status is 0 unless  an  invalid  option  or  argument  is
              supplied, or an error occurs while setting a new limit.

       umask [-p] [-S] [mode]
              The  user file-creation mask is set to mode.  If mode begins with a digit, it is interpreted as an octal number; otherwise it is
              interpreted as a symbolic mode mask similar to that accepted by chmod(1).  If mode is omitted, the current value of the mask  is
              printed.  The -S option causes the mask to be printed in symbolic form; the default output is an octal number.  If the -p option
              is supplied, and mode is omitted, the output is in a form that may be reused as input.  The return status is 0 if the  mode  was
              successfully changed or if no mode argument was supplied, and false otherwise.

       unalias [-a] [name ...]
              Remove  each  name from the list of defined aliases.  If -a is supplied, all alias definitions are removed.  The return value is
              true unless a supplied name is not a defined alias.

       unset [-fv] [name ...]
              For each name, remove the corresponding variable or function.  If no options are supplied, or the -v option is given, each  name
              refers  to  a  shell variable.  Read-only variables may not be unset.  If -f is specified, each name refers to a shell function,
              and the function definition is removed.  Each unset variable or function is removed from the environment  passed  to  subsequent
              commands.  If any of COMP_WORDBREAKS, RANDOM, SECONDS, LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are unset, they lose their
              special properties, even if they are subsequently reset.  The exit status is true unless a name is readonly.

       wait [n ...]
              Wait for each specified process and return its termination status.  Each n may be a process ID or a job specification; if a  job
              spec is given, all processes in that job's pipeline are waited for.  If n is not given, all currently active child processes are
              waited for, and the return status is zero.  If n specifies a non-existent process or job, the return status is 127.   Otherwise,
              the return status is the exit status of the last process or job waited for.

RESTRICTED SHELL

       If  bash  is started with the name rbash, or the -r option is supplied at invocation, the shell becomes restricted.  A restricted shell
       is used to set up an environment more controlled than the standard shell.  It behaves identically to bash with the exception  that  the
       following are disallowed or not performed:

       ·      changing directories with cd

       ·      setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV

       ·      specifying command names containing /

       ·      specifying a file name containing a / as an argument to the .  builtin command

       ·      specifying a filename containing a slash as an argument to the -p option to the hash builtin command

       ·      importing function definitions from the shell environment at startup

       ·      parsing the value of SHELLOPTS from the shell environment at startup

       ·      redirecting output using the >, >|, <>, >&, &>, and >> redirection operators

       ·      using the exec builtin command to replace the shell with another command

       ·      adding or deleting builtin commands with the -f and -d options to the enable builtin command

       ·      using the enable builtin command to enable disabled shell builtins

       ·      specifying the -p option to the command builtin command

       ·      turning off restricted mode with set +r or set +o restricted.

       These restrictions are enforced after any startup files are read.

       When  a  command  that is found to be a shell script is executed (see COMMAND EXECUTION above), rbash turns off any restrictions in the
       shell spawned to execute the script.

SEE ALSO

       Bash Reference Manual, Brian Fox and Chet Ramey
       The Gnu Readline Library, Brian Fox and Chet Ramey
       The Gnu History Library, Brian Fox and Chet Ramey
       Portable Operating System Interface (POSIX) Part 2: Shell and Utilities, IEEE
       sh(1), ksh(1), csh(1)
       emacs(1), vi(1)
       readline(3)

FILES

       /bin/bash
              The bash executable
       /etc/profile
              The systemwide initialization file, executed for login shells
       /etc/bash.bashrc
              The systemwide per-interactive-shell startup file
       /etc/bash.bash.logout
              The systemwide login shell cleanup file, executed when a login shell exits
       ~/.bash_profile
              The personal initialization file, executed for login shells
       ~/.bashrc
              The individual per-interactive-shell startup file
       ~/.bash_logout
              The individual login shell cleanup file, executed when a login shell exits
       ~/.inputrc
              Individual readline initialization file

AUTHORS

       Brian Fox, Free Software Foundation
       bfox@gnu.org

       Chet Ramey, Case Western Reserve University
       chet.ramey@case.edu

BUG REPORTS

       If you find a bug in bash, you should report it.  But first, you should make sure that it really is a bug, and that it appears  in  the
       latest version of bash.  The latest version is always available from ftp://ftp.gnu.org/pub/gnu/bash/.

       Once  you  have  determined  that  a  bug  actually exists, use the bashbug command to submit a bug report.  If you have a fix, you are
       encouraged to mail that as well!  Suggestions and `philosophical' bug reports may be mailed to bug-bash@gnu.org or posted to the Usenet
       newsgroup gnu.bash.bug.

       ALL bug reports should include:

       The version number of bash
       The hardware and operating system
       The compiler used to compile
       A description of the bug behaviour
       A short script or `recipe' which exercises the bug

       bashbug inserts the first three items automatically into the template it provides for filing a bug report.

       Comments and bug reports concerning this manual page should be directed to chet.ramey@case.edu.

BUGS

       It's too big and too slow.

       There are some subtle differences between bash and traditional versions of sh, mostly because of the POSIX specification.

       Aliases are confusing in some uses.

       Shell builtin commands and functions are not stoppable/restartable.

       Compound  commands and command sequences of the form `a ; b ; c' are not handled gracefully when process suspension is attempted.  When
       a process is stopped, the shell immediately executes the next command in the sequence.  It suffices to place the sequence  of  commands
       between parentheses to force it into a subshell, which may be stopped as a unit.

       Array variables may not (yet) be exported.

       There may be only one active coprocess at a time.
 

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